I've defretted a maple fb with what i think was a poly finish, and all we did was to smoothen the finish down very lightly with 240 grit sandpaper, and then a good rub with a scotch brite. Did not remove it, and we just put the CA (superglue) finish on top of that.
Its held up well for quite a while now, so i dont think its a problem.
But i would recommend epoxy instead of the CA glue. Much easier to work with.
Hope you can use this information for something. I am by no means an expert but i have done 2 defrets.