The following is a guide made from my own observations, together with excellent technical feedback provided by Randall Benson; information and images found on Kevin Chan’s Seiko Diver’s Reference; and further feedback [most notably from] from Luka-San, Cobrajet, and too many others to mention. I flagrantly "borrowed" some pictures that were posted to the forum, I hope you don't mind my using them here. Thanks all of you for your inputs.
Please note that the guide focuses solely on 6309 dive watches and does not address the Japan only 6306 variant of the watch.
Please feel free to add any information and images you feel are worth adding.
http://forums.watchuseek.com/f281/how-buy-seiko-6309-diver-collectors-buying-guide-140799.html