shoejoe. Those tunes are kown as “misinai” as an expression they arent litterally from Sinai.
As to the OP’s question outside of written word it is hard (impossible?)to pass down a mesorah over that long a period. Think of tzaras/exact color of techeiles which have been lost over the years. Even within the written word think how many machlokasim have arisen over the years, even involving basic things like sounds of shofar, orders of parshiyos of tefilin, of course explanations have been given as to how those disagreements arose, but the interuptions/confusion/disagreement in our mesorah is real (we have ways to deal with it, his isnt a question). Even within the written Torah their are differences between ours and chazal’s and even among ours their are 10 differences between most of ours and Teimanim (the most well known of which is Dakah with a “heh” or “aleph”) That tunes have been lost is o be expected.