Or it could be a I IV with the Bm being the I chord, and the E being the IV.. this makes even more sense, since the Bm blues scale sounds wonderful over these chords.
Just like Oya Como Va by Santana - Am to D7 - which I would always consider to be in the key of Am, since it never resolved to G.
Yeah, you’re right about Santana. That would be a I chord to a major IV chord in the key of A minor (Am — D). However, the IV is a minor chord in the minor Key. So technically it would be Am to Dm. And there are songs that have the IV chord as a minor. “Baby Please Don’t Go” is an example of having a minor IV chord. And minor blues also have a minor IV chord (The Thrill is Gone).