Z Heads, 915 casting, 10139 date code?

Okay, looking allpar.com says the 360 was produced from 1971-2002. How to explain a set of 'Z' heads, casting number 3418915B (missing the 5 in some places!?!), also has the AAWJ360, but with a production date code of 10139? Isn't that Oct 13th, 1969?

I just had these reworked, but before tear down, they appeared to have factory 2.02 valves.