Also, if very literate Tanomo wrote down stuff and that stuff was passed on to Takeda, Takeda would have no need to memorize what he received, other than what the written stuff signified knowledge wise. Rather, he could just employ someone to copy his Tanomo writings when that transference was called for.
That is huge "if" I realize. If the enrollment books were displayed, why not share any scrolls passed on to Takeda from Tanomo? They wouldn't have to display the contents, only the existence. It would certainly make tracing the history of the "Ryu" a heck of a lot easier . . . hmmm, maybe that's why . . . .
Oh well, don't mind me, I argue with myself all the time!