Hi philkid:
I won't comment on the authenticity, or otherwise, of this sword but will just make a few observations. The extensive corrosion to the blade is a direct result of burying it and allowing moisture, acidity and other harsh chemical reactions to seriously damage it. This makes evaluation of the blade's age very difficult. [It would also greatly reduce my interest in purchasing such a sword and the amount I would pay for it

-- that's a personal opinion, of course, and others may feel differently.]
The relatively well preserved hilt of wood and brass seems out of keeping with the state of the blade, but it is possible that the hilt was better wrapped or preserved and so survived burial in a better state. It might also be a recent replacement for a damaged original. You should be able to tell if this is a recent replacement by looking where the blade enters the hilt for any recent fixation with epoxy, pitch, etc. The absence of an iron handguard, or the holes where one once was, is not a very good indicator of age because some of the older ones did not have such a guard (or the holes). Newer hilts generally lack those holes, as you point out.
The use of brass on the hilt, and perhaps the presence of inlaid brass dots at the end of the blade, are 20th C. features IMHO. Brass on the hilt especially tends to be a mid- to late-20th C feature, perhaps also a little before WWII, but I have not seen this style of hilt on a Kampilan 100+ years old. The hilt suggests Maranao work to me.
Overall, I don't think this blade is much older than the 1930s, and the hilt could be more recent than that. The sword has suffered harsh treatment which makes further identification difficult. Hope this is helpful. You may well get different opinions from other forumites.
Ian.