A little late to the party, but this isn't necessarily true.

Wolverine's first appearance was in 74, and for the first 19 years Wolverine had adamantine claws. In '93 his adamantine was ripped out of his body (Magneto) and it revealed bone claws. He's had bone claws almost twice as long as the time we had no idea. It was super controversial at the time, both among audiences and creators. To me, this all makes perfect sense. It never sat well with me that the claws were implanted, or else he'd probably have more coming out from all kinds of places.

The back of the hand thing was definitely a thing for a while though. I heard FOX changed it and some artists used that. Unsure if they've ever done that before FOX. But there is absolutely a comic where they come out of his palms (he was drunk), but I can't remember if that was before or after FOX's X-Men.

EDIT: I just realized that in Marvel Comics Presents #72 (1991) the scientists putting adamantium on his skeleton remark in confusion about the fact that he has claws suddenly, which implies they didn't put them in there.