Just an educated guess at this point. I will have some more confirmed info for you later but right now I can tell you that I know for a fact that these numbers from Yugo kits correspond with these production dates. Also, your gun could have been a stamped gun before they demilled it.
Consider it an educated guess based on the following:
Bolt with #181052 from a 1983
Bolt with #506111 from a 1988
Bolt with #664790 from a 1990
very interesting, I'm also interested in possibility of it being stamped before demilled, lets hope google wont fail me this time