I may have spoken too soon on Australia and New Zealand. There is an interesting table at this link:
Which gives some standard sizes based on Grade. It states that these are the nominal beam widths and depths, I'm not sure if that is the actual size but I will assume so for now.
Some of these depths would suggest that the typical ply thickness is 30mm however there are also quite a few depths where this 30mm does not work. Either there is a different ply thickness for these other depths or they are planing down the larger beams to get to this size.
For example within GL18 the following depths exist: 270, 280, 300, 315, 330. 270, 300, and 330 fit nicely with a 30mm ply thickness, how is the 280 and 315 constructed?