Bill, I'd guess three of those from Sulu and two from central Mindanao - so that's no help, but it does show that it wasn't characteristic of one particular locale. The question would be from those of you that are lucky enough to have several of these (and Bill it looks like you have more than your share
) can we determine by dating if it spread North of South. Unfortunately Jolo and Cotabato were both major trading ports during the time most these were probably manufactured.