I am continuing to go through my collection and ran across 3 new old stock IBM keyboards from PC-XT days. I see no numbers on the keyboard itself, but the box is labeled as a model 1501100. I see references to this model sometimes being referred to as a Model F and some fairly high prices for Model F keyboards. Do any of you have information on identifying model 1501100 or Model F keyboards? I am hoping I have a couple of valuable keyboards!