I've gone through the thread a bit to try to nail down the edge of where "legit cover" ends and "not a cover" begins. The word "bootleg" has only appeared in this thread once, so the ground's not quite been thoroughly covered just yet.
I'll lay out a few scenarios in sort of a spectrum, going from "no question that's a legit cover!" to "ummm???"
1) The song was commercially available on a studio album, single, or non-album single -- COVER
2) The song was commercially available on a live album, single, or non-album single -- COVER
3) The song was commercially available on a special-edition studio/live album, single, or non-album single -- COVER
4) The song was commercially available in, e.g., a box set, special edition, import, an album of outtakes, or similar -- COVER
5) The song was not commercially available, but was released digitally by the artist, label, songwriter, publisher, or copyright holder -- PROBABLY A COVER?
6) The song was not commercially available. It was released digitally by an entity affiliated with the artist but with dubious, gray-area sanction (e.g. by a fan club/website, or something a studio employee uploaded to YouTube) -- NO IDEA
7) The song was not commercially available, and was only ever available via bootleg recordings -- NOT A COVER?
8) The song was not commercially available. Someone in the smartphone era recorded a live cover performance at a recent show, and uploaded it to Youtube -- ???
What does the house think -- especially songs that fall into the 5, 6, 7 , and 8 categories?