Pardon my ignorance, but if update/backdate is not itself the intent - to allow later assemblies (update) from the specline to be used with older assemblies or in older cars or vice versa (backdate) - than what is the point of having that statement at all? I've always read this rule to say that, for example, a late model induction could be attached to a early model long block in any year body from the spec line, so long as all parts are from that model and that specline. If the intention is otherwise, than the statement needs to be reworded - updating does not to me, and apparently many others, mean "newer but identical assembly," but "newer, different assembly used in later cars of the same trim and body style on this specline."

I would think that the same would apply to transmissions and bodywork. thoguh I would say in the case of the latter that the full model year's body should be together. I would agree that parts and assemblies specific to a certain body type would be allowed only with that body.

the VIN rule was, to me, a way to keep a car from being converted to a different model - i.e. a civic DX from becoming a Civic Si. I wasn't privy to any of the decisions revolving around removal of this rule, but I assumed it has more to do with the lack of differences when prepared to the ITCS.