The thing am still finding out about these blades is the 'humpback' feature at the spine (the right end of the red dotted line in the att. pics).
Am not sure if this humpback feature points to a particular province or region in Luzon. Alternatively it can be a style that was broadly used. Am still not sure either way. Perhaps more pics can be posted in this thread so we put our minds together
p.s. - the pic with dark background is from erik farrow. the one with very light background is from artotec of ebay. thanks.