There's a lot written about dating of components in the CRG articles. Click on the red rectangle at the top right corner of this page.
I agree that it is noble to try and get as close as you can to an original dated engine, parts and/or transmission. What I feel is negative is, the way some people can seem to get stressed out whether or not their non-original engine is dated just right for their cars build date. To me it just seems irrelevant, as I stated above, it's either the original one or not. There are examples of dates that fall out of the normal guidelines and if your components are original to the car and you can back it up, that's just the way it happened on that particular car, etc. For example, If you have an original engine that is cast, say, 6 months before it was assembled, and you can prove it was the original engine, then you have nothing to prove anymore. It's just the way it happened. But if you have a non-original engine cast 6 months before your car was made, then you will have an endless supply of opinions that that is way too early for your car. To me it just wouldn't matter if I didn't (and I don't ) have the original engine, what the dates were on it. If you have a 69 Z and have a DZ 302 in it that isn't the vin matched engine, all that would matter, to me, is that it has a real 302 in it with all the correct parts. It would be worth the same to me (less because it doesn't have the born with engine) if the engine in it was dated before the car was built or after.