While I know that the rule seems to be seperate gangya = pre 1930, however I got the sense from most of those that I talked to in Sulu reference these that the seperate gangya was more of a guarantee of it being older, however they felt that the one piece blade was also made by many prior to the magic 1930 mark also.
A while back it was stated in this forum that there are still kris with separate gangya being made - not only in Indonesia but also in the Sulu archipelago. (This observation coming from Carlos if I remember correctly.) Could you folks on Jolo try to get further info along these lines?
While Stone's rule of thumb (separate gangya: likely pre-1930; integral gangya: most likely 20th c.) seems to work out ok most of the time for Filipino kris, we apparently have to take into account exceptions in both categories.
I still wonder how this integral gangya syndrome could spread that fast throughout Moroland (in just a few decades). I'd have expected a much more patchy/localized development with older pandays clinging to the traditional design until their demise...