Cross-referencing what's out there on the internet, it appears that this album discography is indeed complete. Far fewer titles than I'd initially thought. The series began with vinyl, cassette, and compact disc; the first two formats eventually fell away, and the compact disc series stretched until 2001. There were apparently some represses in 2006, but apart from that, the entire series appears to be out-of-print. Some titles (Hooker, Hopkins, Lonnie Johnson) are still available used on eBay and Discogs while other titles (Pete Franklin, Baby Tate, Arbee Stidham, Sidney Maiden) are pretty rare—meaning, high prices on the used market. The U.S. vendor decluttr on eBay has had some OBC titles at decent prices. I was able to pick up the two Roosevelt Sykes titles this way.
One caution—as with the OJC series, it's possible that some OBC titles listed as "new" are in fact CDR's, which complicates collecting (if you don't want a CDR). Then again, I rolled the dice on a "new" title recently, and it ended up actually being old stock from 1993.
I only had a few titles from this series, and am just now exploring the breadth of its discography. The recording quality on the whole is excellent. I've given so much of my attention to blues from the 20's and 30's that I've overlooked this revival period. Definitely some gems within. The Pete Williams, as one example, is raw and brilliant. As I get to know this series more broadly, I hear the influence of Patton, Blind Lemon, Tommy Johnson, and of course Robert Johnson as a sort of bedrock. I also realize how little I know about artists such as Otis Spann or Memphis Slim, and that there are considerable holes in my understanding of the evolution of blues music from the late 50's to the mid-60's. Part of the fun, of course, is filling these holes in!