Yeah, I'd think the 12 inch Lexington address (up to BN 1542, Sonny Rollins Vol. I?) and the W 63rd titles are among the rarest, because of the original maunfacturing and pressing of the these products, such as the flat edge, the ear, the deep groove, microgroove, mono, etc., and the number that were actually pressed. I could be wrong about this, but that seems to be the case when these BN's are auctioned off on Ebay. It seems that BN 1542, 1560 (the Mobley) and Tina's True Blue are among the rarest.