Complicated to exploit bugs often rely on specific code and data being in particular places or even the number of cycles a code block takes so even if the same

Complicated to exploit bugs often rely on specific code and data being in particular places or even the number of cycles a code block takes so even if the same bug had existed for years you might have to write a separate exploit for each version. And make a version check if failed attempt will crash the software or you only get one attempt. Sometimes the hardest part is finding out what version of exploit to use and that may even have to be done manually.