I know that the style of the strap has changed over time. Earlier Basic Bags have a double strap and newer ones have a single strap. The earliest Basic Bags have a very heavy industrial TALON zipper but Coach started using a lighter YKK zipper for the Basic quite some time ago.
I just bought a vintage basic bag on ebay. It needs some of the brass cleaned and it could use some cleaning and moisturizing. Any tips? I also posted on a thread that I think it's yours, coincidentally, called Rehab Bonanza.