Came across my 1st Vette re-stampings in the '70s - problem being, most guys decking the blocks went through the #s.
Some were legit, really the car's original block; but the "economic opportunities" were immediately obvious, and became more pervasive.
Getting the right casting # has also been a big deal in Vette circles for decades.
Since then, it's evolved to a point where I wouldn't trust any Vette to have its original engine unless I knew the car has never been apart.