Hopefully Mark M. has some input as to known or rumored fakes of this West Coast issue. The backs are definitely different than previously known examples. There is some similarity among Standard Biscuit, Holsum and Herpolsheimer to suggest that the same printer was involved in all three sets and yet as Rhett said these from ebay last night lack the clarity and evenness of printing found in the others. The cards also looked a bit too white or "un-toned" to me also, although the '21s show less toning than the '17s (see Leon's post) and it could just be the scans.
If it's a stamp it's a very intricate one; otherwise it could just be a less precise printing from a different printer--we know there were at least two printings of this set because of the "80 photographs" language found sometimes. Still, apart from the uneven inking, what also bothers me is the inconsistent printing/inking within the various cards themselves that sold last night. One looks generally washed out, no bold distinction between "Standard Biscuit" and message text, blurred "Cal.", another looks a little more heavily inked on the right-side letters and frame, another on the left, etc. A different printing would not show such inconsistency would it? This too supports a stamped backing, and although that would not mean they were fake per se, it would really make me skeptical that these are period with genuine backs (although I'd love to have one or two in hand to see)
