Whereas I agree 100% with what you are saying, not everybody knows (or cares) that the date on the tag may not be the actual date or the correct terminology to word a question.
I stand on my opinion that on earlier cars it is all we can go on and when most people ask about the build date it is good enough.
Answer the question the best you can with the information that you have, if the scheduled production date is all you have then that is the best you can do.
Its not like we are going into the DMV and lying about our age, the actual production date is meaningless, it is just a novelty.
Alan