It's easy to see which mode many chord progressions are in. For example, I-IV is Ionian; i-iv is Aeolian; i-IV is Dorian, etc. But I'm not sure how to analyze some progressions. For example, I-bVII-IV, I-bIII-IV, Ib7-IVb7, Ib7-IVb7-Vb7 (dom.7 blues). Are these simply "pop/blues conventions" that don't follow any specific mode?