You might like Bartok and know the more famous works (which are amazing) but did you know he was an avid cataloguer of folksong? He made many recordings of Hungarian folksong at a time when modernity had not yet reached the villages, so to speak. I learned this by reading a biography years ago. He notated the songs as accurately as he could-- if you see what he wrote down he tried to catch every inflection and rhythmic stretch or shift.
Two more things 1/n
First check out his "improvisations on Hungarian folk tunes" it is incredible and I had never heard of it before-- found it on a streaming service.
Second does archive org have digitization a of the cylinders? I think I read in this biography (itself very old) that like the Hungarian national Library held them or something. These are incredible musical treasure if they exist.
The recordings were made on cylinders which were sort of a precursor to phonograph. Imagine a cylinder that a machine etched sort of like vinyl. I have never seen one in real life but the point is Bartok went to many villages and made these recordings to try and capture and art form before it changed or disappeared.
Kodaly also wrote down a bunch but-- Bartok felt he missed too much of the details. I guess the Kodaly transcriptions are, well basically "quantized." (Pitch and rhythm)
PsySal