Tuners and uke age

I like vintage soprano ukes and wondered if they could be dated by tuner type and color? Assuming that the tuners are original, when did the various makes stop using wooden tuners, anyone know? I've also noticed that some 30's ukes have a very art decoy looking tuner, more angular than round and later ukes have a Ping looking oval tuner buttons. I've also noticed that many 20's and 30's ukes have black buttons and this seems uncommon after 1950. For example, according to Tom Favilla, 80% of Favilla U2's made before 1945 had black buttons while those made after 1945 had white buttons. Anyone else have info like this on other brands? cheers, g2