In the late 80s I was working in Manhattan and a guy showed me a bunch of gold chains that had these little tags that said 14k..I think I bought 5 of them for a $100 that looked just like yours..What a score I thought until a week later the one I was wearing turned green.
Took them to a jewler and he said the tag was in fact 14 k,but not the necklace..He also said the tags are sold for like $10 a box,they are thin and they just kinda dangled on the clasp...At least you found yours,I bought mine.lol..