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This card used in 1924 has a "U" in the middle of the Kodak Austral "stamp box".

This example is dated 3rd June 1931 - note that the T is absent (or just about) from AUSTRAL on both sides.
This is most likely to be of no importance whatsoever but if we can find another card with a similar "fault"
it may turn out to be of significance for "dating" purposes.

This card is dated 1928 - note that the cross is absent from all but the UR corner

This Kodak Austral card was printed in 1912 (RP view of "S.S. Oonah" on the rocks" by E. Winter)
The printing is more ornate (Art Nouveau style?) than the post-WWI cards and the "stamp square"
has dots instead of crosses in the corners.

This card dates from 1933 - the photo is a view of the H.M.A.S. Australia in port at Burnie during March of that year.
Card mostly likely to have been produced by Ernest Winter

This card is dated 1916.

Assuming they are not later prints, these cards date from 1926 as both have cast photos taken during the screening "
For the Term of His Natural Life" at Port Arthur during August/September of that year.

This card was used in 1922 and has what appears to be "18" or "1B" or similar in the stamp box.

Tasmanian card with message dated 1919 - thanks Mike!

1926 - on back of souvenir card prepared for the world tour of the "Australian Ladies Pipe Band".

This card is dated "1913" and is of Tasmanian origin.
[attachment=0]kodak 1913.jpg[/attachment]

To see all of this interesting card proving that "Budgie Smugglers" as a popular style of
swimming costume had a predecessor, follow this link: http://tps.org.au/bb/viewtopic.php?f=6&t=489#p2043

This card is from 1923 and has an 'R' in the stamp box with crosses in all corners.
[attachment=1]e100a.jpg[/attachment]
[attachment=0]e100.jpg[/attachment]

This card from 1905 may pre-date the introduction of "Austral" photo postcard stock
It is probably of British manufacture as I have not seen any cards originating from the United States with this back.
"For Inland Postage Only..." inscription on verso suggests this as well.

Doe anyone have any Tassie views printed on this photo stock?

This card of a snowfall in Franklin Square, Hobart is dated "July 1922" - the Kodak Austral 'stamp box' has a cross in all corners plus the number '7' printed within.

I have just started looking through a collection of old family photos and found this to be the site with the most comprehensive set of information on this topic. Mine are nearly all from Brisbane, but I doubt that will make any difference.
Most are studio photos of people, and of course, most have no date. I have checked over 50 Kodak postcards so far, with 16 that I have a definite date and 2 where I am reasonably confident of the date, assuming I have the right person.

Because most are studio photos, I presume they would have a fairly high turnover and relatively fresh stock. Even so, I can see no obvious trends with dating, apart from the obvious early K-A series. I have none of the later K-G or K-H type. The known dates of all my cards cover the range from 1912 to 1927.

Most common: K-D

By far the most common card (over 70%) are the K-D type - all letters the same size and with 4 crosses. These are divided roughly 50:50 between those having an internal number or letter and those being blank.
I have looked at the interior numbers and letters for K-D style but can discern no useful trends. Lower numbers tend to show up in earlier photos, but I don't have a big enough range to tell - I have seen none outside the range 1919 to 1924. Certainly the blanks, letters and numbers overlap in time. I have blank K-Ds ranging from 1915 to 1937.

Big K with 4 crosses

The next most common is not even listed in the Peterson/Stalley table: that is a large K for the last letter of Kodak in the top row, and having 4 crosses - see next image. I have them with interiors blank, with numbers and with letters.
This design ranges from 1922 to 1931. The blank internal version covers this range and the numbers and letters occur within that range.

Other unlisted styles

I have undated examples of yet two more styles not in the Peterson/Stalley list. They are based on K-D, but have only 3 crosses. and I am beginning to wonder if all these variants with fewer than 4 crosses simply represent instances where the type has fallen out, broken off or otherwise not been inked properly.

Typography

Other changes that I have not seen commented elsewhere are with the typography. These next three images show that, even with a single design (K-D), different fonts were used at different times - or maybe even at the same time. There is a general trend for later cards to have a finer font, but again it is not clear-cut. It is not simply a case of the type wearing out, or different amounts of ink being applied because not only does the stroke thickness change, but the width to height ratio also changes.

Cross shapes

A final observation relates to the crosses themselves. A very specific shape was used, as you can see in my first scan - I'm sure it has a specific name, but I don't know it. Playle's site, for example, lists corner shapes being either diamonds or elongated plus signs. The "diamonds" I am sure are simply this cross with excess ink running into the diagonals.
As for any being like an elongated plus sign, I have seen a few that could be taken for that (such as the bottom line my the last image), but I think it more likely that they are from worn or damaged type.

Unless we can collect and analyse many hundreds of these postcards, I think we are limited to the following conclusions, based on the contents of this thread.

The number of corner crosses, whether deliberate or accidental, offers no useful information for dating purposes and can be ignored.

The internal letters and numbers might have useful date information, but we have not collected enough to know.

The following designs and dates are known, with date limits not being guaranteed.
Because of the unnecessary complexity in Peterson's naming together with missing designs, I decided to use a different scheme.

Unless otherwise stated, all have "KODAK" along the top and bottom of the stamp box and "AUSTRAL" running down the left and right sides.

Type KP-1:

• Peterson's K-A and K-AA
• design: solid circles in corners, heading with or without scrollwork.
• first seen: 1908
• last seen: 1914

Type KP-2:

• Peterson's K-B, K-C, K-F, etc
• design: Crosses in corners; last letter K of top line is enlarged
• first seen: 1913
• last seen: 1933
• almost all are in the 1920's
• interior of stamp box can be blank, or have a letter or number (22 is largest seen)

Type KP-3:

• Peterson's K-D, K-E
• design: Crosses in corners; all letters are the same size
• first seen: 1915
• last seen: 1940
• interior of stamp box can be blank, or have a letter or number (19 is largest seen)

Type KP-4:

• Peterson's K-G
• design: Crosses in corners; all letters are the same size; word "KODAK" replaces Austral
• first seen: 1920
• last seen: 1930

Type KP-5:

• Peterson's K-H
• design: 5-pointed stars in corners
• first seen: 1945
• last seen: ?

I have a KODAK AUSTRAL Postcard which I would like to try to date. It of Type KP-3 (Peterson's K-D) and the interior of the stamp box is blank. Your evidence suggests that this style was first seen in 1915 and last seen in 1940 - that's a wide date-range!

The postcard is an undated studio portrait of a woman and bears an embossed symbol identifying the studio as that of Poul Poulsen, Brisbane.
Poulsen Studios advertised regularly in the 'small-ads' of The Telegraph, Brisbane, but the first evidence I can find of their advertising Post Card Photographs is a 'boxed advert' in The Telegraph (Brisbane) of Sat 12 Jan 1918.

So maybe I am now narrowed to 1918 to 1940 - but that is still a wide date range!

However, within the stamp box there is the number '1723' hand-written, in pencil. Maybe this is a Poulsen Studio serial or account number?
I wonder whether any other member has a Poulsen Studio, Brisbane, Post Card Photograph with such a 'serial' number, and which carries some other clear dating reference? If so that might indicate whether my card was produced before, or after that date . . .

I have found only seen one Poulsen studio card in my collection. It is dated 1921 and has no detectable pencil codes. It has a printed '8' in the stamp box.
It is a studio photo of a baby of a friend of the family, so I would guess the parents had many copies made, and so I would not expect the studio to mark every one.

It has the same embossed design as yours - I wonder if their stamps changed over the years and that might provide a clue. My only other Poulsens were large prints where the embossing was on the matte or things like Paris Panels, where the studio name was on the bottom strip of card. So they don't help.

You might try the State Library or John Oxley collection for Poulsen prints.

Cameron, thanks for such a speedy response.
Your Poulsen card is interesting. I wonder if anyone else has such a card?
On my card, the Poulsen Studio embossing is approx. 5/8 in. (16.6 mm) in diameter.
The monogram in the centre is distinctly the entwined letters PCP. Poul Cristensen Poulsen actually died in 1925, but his sons and a grandson continued Poulsen Studios in Brisbane:
N. H. Poulsen (son of Poul): Poulsen Studios Brisbane w.1915 - 1920s
William Poulsen (eldest son of Poul): Poulsen Studios Brisbane 1909 - 1950s
William C. Poulsen (son of William Poulsen): Poulsen Studios Brisbane 1900 - 1950s 
The Telegraph, Brisbane Fri 15 Dec 1916 cites the form of P.C.Poulson & Son at 11 to 18 Queen St. Brisbane
The Telegraph, Brisbane Sat 13 Dec 1924 identifies NH and WC Poulsen as the proprietors of Poulsen Studios at 18 Queen St. Brisbane.
I wonder whether they continued to use the PCP monogram after he withdrew from the business?

I'll now try to follow up your suggestions.

If this is of any help: I have a postcard printed on type 'D' paper. Date of the photograph is apr 1925, the subject is two polar bears at Beaumaris, which arrived in 1924 as cubs, and in the photo the animals are still sub-adults. The card itself was purchased and sent sometime after 1932, there's no date in the text, but the novel 'Inheritence' by a Dr Phyllis Bentley, and which was first published in 1932. There is one digit '3', next to 'OZ' remaining of the post mark from where it must have been franked beyond the stamp, which has been removed, I'm assuming this suggests 1933 as a date of sending.

Apologies for the poor quality.