Clearly it doesn't happen often; but if someone makes a significant contribution to a paper the length of time it took to produce is irrelevant. It has happene

Clearly it doesn't happen often; but if someone makes a significant contribution to a paper the length of time it took to produce is irrelevant. It has happened before to non-number-people (e.g. http://www.anoleannals.org/2012/01/03/posthumous-co-authorship-what-are-the-rules/ http://www.anoleannals.org/2012/01/03/posthumous-co-authorsh...), and it doesn't seem like someone added Erdős' name inappropriately..