In your specific example, you can tell because Victoria 3 has buttock actors, and Victoria 4 does not. There are other distinguishing features you might use for other figures (Victoria 2 has an upper neck; G2 figures have a waist actor; and so on) but in general, there's no way of knowing after the fact.

Freebie creators who don't provide readmes are still generous and wonderful people. But I wish they wouldn't shoot themselves in the foot. :)