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GenoAhhh...that makes sense!  I didn't think that they might be different in those two sets, although it sounds obvious in retrospect.  I am still curious about the blank-backed version.  I assume it would be "3B" since the Standard Catalog says the Koester set is a blank-backed Series of 120.  If anyone has a blank-backed Frisch (Koester/W575-1), I'd still love to hear what position it has on it.  Thanks!
Geno