[Gustav]

Regarding the seldom seen Central Javanese form, I have no difficulties to find another one in van Duuren's book, and yet another one from ACM in Singapore, and I even have not started to comb the bigger databases for related forms.

Why it is seldom seen? I guess, because it most likely was a "special" form (the diamond studded golden Pendoks with green emaille tell about high level Kraton context - the Singapore one is of course different - much simpler Pendok, Madurese hilt, blade actually being a Javanese interpretation of a Balinese Keris), perhaps, like you wrote, at the beginning linked to a certain person - and stopped to be made quite early, most likely already before 1900. I guess every Tukang Wrongko has his own, quite specified repertoire, and if he stops to work and has no follower, that special, rarely encountered form might simply die out. Everything boils down to a few, easily recognizable shapes.