but here's a question: whereas the method books are full of fingering suggestions, the actual publications of music for the instrument enter fingering VERY SPARINGLY. . . . . why????????...........after all, much of the music that was published was aimed at amateurs who could certainly have used a bit of help once in a while in terms of fingering.......
I can speculate at least
Nothing wrong with those 3, but here's a 4th explanation for "sparse" (as opposed to none at all) fingering indications (which ISTR the original post mentioned):
A halfway decent player needs to see only finger numbers that are counter-intuituve, that is, not what he would normally expect -- usually intended to prepare for an awkward note jump or passage that requires exceptions to the "rules" that have been learned.
If there are too many fingerings notated (like on every stinkin' note, as in tutors), the brain just tunes them out as background noise and thus misses the one exceptional finger that was really needed.
Notating just the oddball fingers makes them more likely to be noticed.
This observation is from my piano experience, but it seems to apply to my 'tina scribblings too.
Oh yes, the Mayans had ceramic flutes and the zero, but all their music tutor books were burned by the Spaniards, so we'll never know how they numbered the thumb