Or a library who's code now only exists on the wayback machine... and of the modified version that you actually use only a single copy exists on an old machine

Or a library who's code now only exists on the wayback machine... and of the modified version that you actually use only a single copy exists on an old machine that one of the devs in the company never bothered to hand in for recycling... Never mind that it's part of a decade old contract stipulating a quarter century support... Greenfield is easy. :)