[burrahobbit]

With Middle-earth stuff there are many varying levels of canon. The most canonical is LotR, it is one of the things used to judge if something else is canon. The other thing is author's intent. I may not be very far off base if I were to say that BoLT is the least canonical work that has been published. By the end of his life Tolkien had abandoned or modified nearly every aspect of BoLT. In my mind The Silmarillion, parts of UT, and parts of HoME inhabit the same level of canon, just lower than LotR. After that, in the third level down, is The Hobbit and much of the rest of UT and HoME. Then the remainder of UT, HoME, and the majority of BoLT. Keeping in mind that the order after LotR is just my opinion, and subject to change.