Assume for the moment that a "reasonable" "historic" letter order is that found in Doctrina Cristiana:
A U E H P K S L T N B M G D/R Y NG W
Also for the moment, assume that our originator of this script lumped a few "leftover" letters at the end, following an order similar to Rejang and Bugis, for R, Y, and W, inserting NG between Y and W (and not too far removed from Kerinci, Lampung, and Sundanese, either).
Leaving the vowels alone, that leaves a potential mnemonic in the remaining consonants:
H P K S L T N B M G
Assume yet further that S-L is SU-LA "Sula(t)", a letter, a note, a jotting.
Then we have the following word-puzzle:
H P K SuLat T N B M G
Sadly, I'm not fluent in Tagalog of any era.
T-N /TiNu/ 'taught' ?
"HaPa(k), Ko SuLa(t), TiNu" B- M- G-
"broken, I have written and taught" ?
Of course I'm worse than a fool for even posting that attempt.