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Things like glass dates and even the serial number will only allow an approximate build date of your vehicles.
Glass was made in huge batches and installed upon the assembly line, in some cases, for months prior to another batch being produced. That is precisely why most cars have glass with dates that vary as much as three months. that's my experience anyway - others may have witnessed even larger gaps.
The engines and transmissions were built and assembled as a "unit" whereupon a serial number was affixed. Those assemblies were then sent to various plants / assembly lines all over the country.
There are no positive records that tell us how quickly they were installed.
As far as 'early" and "late"... those are simply terms tossed around by folks in the hobby and have no real definition.
Some design changes occurred nearly the day the first of a model rolled off the assembly line. Others occurred weeks, even many months later.
The best you can hope to do for "correctness" is attempt to determine approximately when your car was assembled and when noticeable changes occurred.
Referencing engineering releases may possibly be the best (most accurate) way to determine when changes occurred. But even then, some plants didn't make the changes as quickly as others. And, it's been documented that some changes occurred prior to an engineering release being signed off upon.