Apparently we're the only ones with too much time to think, DJ.
Obviously, I'm free to be corrected, but the rough mud-map as I understand it:
1. The Poms started with pre-65 because it was when their industry still had some relevance, and they had lots of bikes with a lot of knowledge sitting idle.
2. The pre-75 thing came about because that was the end of the short-travel era - yeah, there was a very small handful of (relatively) LTR bikes in 74, and quite a few short travel 75+ models, but 1975 was the obvious turning point.
3. Then pre-70 made sense, partly because it was the era where the Euros dominated and partly because it evenly splits the other two classes.
4. After that, pre-80 was established by the Victorians because it was a good idea, and because it suited the next era of VMX racers.
5. Seeing its success, other states followed, but used the USA model where all bikes of a similar, pre-80 type spec are in the class together regardless of age (ie: Evo).
6. Then someone realised that the 75~77 models were all sitting in shed because they were hopelessly outclassed by the 1980+ bikes that dominate Evo, and pre-78 was born.
7. Finally, enough people realised that pre-85 bikes were older than the pre-75 bikes were when they were first recognised as 'vintage' and they were added.
8. Eventually, enough people will realise that 1990 was a fugging long time ago, and we'll have pre-90 racing (remembering that anybody who's child was born in 1990 can probably already legally go drinking with their child...).
Random points that I can't be bothered to structure into anything like a cohesive argument:
*As much as I like the simple definition of Evo, I can't help but wonder if it causes dramas simply because it is defined so differently than the other classes. Compared to the old pre-80 class, Evo certainly cuts into the numbers in the pre-85 class, at least.
The Victorians have gone with the flow and replaced their pre-80 with Evo. Pragmatically, it is obviously the right decision. Idealogically, I think I like the pre-80 class better.
*In a lot of ways, changing pre-78 into pre-77 makes more sense. The 75/76 (and some 74) models are the real 'not yet sorted' LTR bikes, whereas stuff like the 77 YZs and RMs were very competent second-generation-of-LTR bikes. But a class that caters to only 2 years of bikes (and a couple of Maicos and KTM), won't have enough bikes to make a class themselves. It also means that most 77 model bikes will be fed to the Evo lions.
*Does it really matter that the jap bikes are in with the euros in pre-75? With the exception of the 125 class, the jap bikes don't dominate the euros in this era.
Ah, I dunno. I 'spose its one of those tihngs were even if you did come up with a clearly better class structure, its simply too late to implement because people have bought (and sold) bikes based on the current structure.
At the least, this post should get enough people wanting to correct me that we'll get some life into the topic....