"I like learning new things." (StrawHat)
For some reason, other than ignorance, I wondered the same about a 10-8 I bought used in 1998. It came with the same stocks, only checkered not smooth. The book put the 10-8 manufactured in 1988. They had a date stamped like in the OP, no black washers, and I'm pretty sure (not positive) there were some numbers on one written in pencil but it was illegible to me. I didn't like them in my hand so I bought rubber stocks, which went with the gun when I traded it off. They reside now on my M&P 38 that lettered to 1949 for my grandson. The Magnas were too small for his long fingers. (Of course, since he's only 16 now the gun is with all its friends downstairs.) He loves them. I appreciate the post, also.
I like the way smooth stocks, as the ones posted, bring out the wood grain. But to me they seem too slippery in my sweaty hands in the summer.