This is a very interesting thread Miguel. Thanks so much for all the research.
I am having a difficult time seeing this as anything but an Indonesian keris, in spite of the rectangular tang. The blade bears little resemblance to any other Philippines kris we have seen, but has much in common with early keris such as the blade shape and the carvings which look very much like a double puthut form at the base. There is also, i believe, record of early Indo Keris with square or rectangular tangs. The only thing that remotely resembles a Moro kris here is the tang which isn't very decisive IMO. Clearly trade was in full swing at these times as is evident from the presence of Chinese ceramics also present. So clearly it is possible that this was a blade gained in trade. Even as a traded blade it might very well have become a choice "A" object for the person buried. There is just no telling here.
I would think that if these blades were prevalent in the area during this era that far more than this one single example would have turned up by now. Hardly enough evidence exists to form any opinion of the origin of this single blade let alone to completely reverse the generally accepted theory that the keris developed first in Java before making it's way to the Philippines. Even the evidence of a parallel development is lacking as this seems to be the only example of a "kris" from this time period in the Philippines. Where are all the other artifacts?
