Why is it not considered fraud to advertise the book as being written by Ms. Frank, only to claim another author decades later? They seem to both have their cak

Why is it not considered fraud to advertise the book as being written by Ms. Frank, only to claim another author decades later? They seem to both have their cake and eat it too. I find it especially galling as the co-author died never claiming to be the author. In 67 years time Tom Clancy's third cousin's son no doubt will suddenly appear as a co-author of his books just as they go out of copyright ...