In the case of Allied vehicles the photographic records are fairly good - British armour perhaps less so than American. German subjects can get more speculative, especially in the late war period. But it's a good point; maybe the best approach is a mixture of decals without anything too specific (apart from the names - no harm in using actual names). Then include a couple of templates as indications of where the different markings normally appeared, without trying to represent a specific vehicle.
