I have a B72 with the year (73) stamped into the cantle plate, and a B66 as well - believe it's a 59. Also had a '73 B17 Narrow with the plate stamp.
Others are a "Pre-Softened" Pro with "6C9" and a B17 with "0J6" both in the leather. So, I suppose March of '96 and October of '06?