K17b is unusual because it is the only $5 issued by the Bechtlers that lacks the initial of either Christopher or August. Also, it lacks a star between RUTHERFORD and BECHTLER, which is another eye-ball diagnostic. The 17b designation suggests a subvariety of 17 but, in fact, this is a completely different variety than either K-17 (plain edge) or K-17a (reeded edge). Hopefully, in the anticipated, updated version of Don Kagin's book on Pioneer Gold, this variety will receive the special treatment and recognition it deserves.
Only two examples are known to us. The Allan Collection coin, illustrated above, has a lamination flaw at the base of the reverse (BECHTLER side) but is the finest example known at PCGS XF45.