Well, it depends.

The Mylars were typed & applied near the end of the line. So, if the car was actually made late, it my have the next month on the Mylar.

If it was made early, it may have the previous month on the Mylar.

If there is a registry for your make & model, contact them to see if they have a clear photo of yours.

For folks with 1970 Hamtramck cars I can give you a rough idea of what cars were made closest to yours if you have a broadcast sheet for it.

There is no way to know the actual build date though.