So the period around 1800 is considered to be about the time when these Southern Philippine swords in the form of a keris began to appear?
A bit earlier at least IMHO. How much this extends into the 18th century (and even earlier) is still not well researched yet; the main problem is the scarcity of reliably provenenced museum examples.
Here's an old discussion on archaic (Moro) kris:
So, what would be your estimate when twistcore-like pamor appeared in, say, central Jawa?