In the early 1970's David Baldridge conducted experiments that indicated mammal blood is not particularly attractive to sharks. His studies (he had been maintaining the Shark Attack File) also indicated many shark "attacks" suggested the shark was not trying to feed, but had motives other than hunger for the incidents. Incidentally, of the 1,165
cases in the Shark Attack File (maintained from 1958 till 1969) 1,080 (93.1%) of the attacks were on males, this would seem to indicate blood from menstruation does not attract sharks. I'll look for additional documentation.
As for "common knowledge" - well, it's frequently wrong. In the immortal words (pun intended) of Lazarus Long, "If 'everybody knows' such-and-such, then it ain't so, by at least ten thousand to one."
I've been in the water with sharks on numerous occasions when I've been bleeding from various wounds. To the best of my knowledge I've never had any shark take note of me as a result.
Walter