Metacortex

According to the components and decals (note the different placement of the Cro-Mo decals on the seat tubes) the KGxxxxxx bike was built in '72. You can't date these by serial number alone as the headtubes were stamped with serial numbers before they were even brazed to the frames. I've seen serial numbers that were up to 6 *years* older than when the bikes were actually built. Bottom line: it looks like you have one '71 and one '72.

With a BGxxxxxx serial your '71 model very likely has forged Huret dropouts (with an integral hanger), while the KGxxxxxx '72 model would almost certainly have stamped dropouts without an integral hanger (requiring a claw derailleur mount).