Quoth Re: PT:
I had thought so, too, but checking my copy of The Silmarillion (page 211 in the Ballentine paperback edition), all it says is
and so on, culminating in Huan slaying Drauglin, too, with a bit more effort. So he definitely slew rather a few (unnamed) werewolves (one might even say a slew of them), not just the two biggies, contrary to the good doctor. But the phrasing in the original isn’t even conclusive that he got all of the wolves on the isle (though it does seem to suggest that), and it was after this point that Morgoth picked out Carcharoth from a litter of Drauglin’s get, so it’s definite that there are still multiple werewolves left elsewhere (presumably in Angband).