Difficult in this day-and-age. Stay vigilant. Watch your contracts and agreements, and Google your music every once in awhile to see what's happening.
I have downloads available all over the Internet, and I'm pretty sure that a fair amount of them aren't authorized, but I signed-up for digital distribution with an aggregator and they've got it all over the freakin' world, and I've lost track of what's what. All I know is it makes little difference practically, as it's extremely hard to make any income whatsoever from .00001 cent per play/stream/download, so in practical terms, it's all "piracy" to me, authorized or not.
GJ