I have a tazza with a clear Victorian kite mark which - unless I'm being particular stupid - shows the registration date (1, G, W) for February 1 1878. Checking with the Great Glass site, the closest date that I can find is March 1 1878, a Percival, Vickers design. As the design looks more-or-less identical to a couple of P,V examples pictured on the English Pressed Glass site, I'd assume that this was a manufacturing error. If so, is it safe to attribute to P, V? Would such errors have been common?