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It would appear that the extensions are all, ".MP3" -- which is an industry- standard audio file format. (For example, my soundtrack narrator records my audio scripts and sends them to me as .MP3s -- which I then edit/sync into my videos.)
So -- a global search of the HD for ".MP3" should reveal them -- if the files are not also, somehow, "jiggered"...
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NOTE: Just did that search on my machine. It only turned up video narration files -- and digital audio recordings for an "oral history" done as part of an archaeological project... AND -- the DTG (Date-time groups) in the filenames are exactly as Mr170IQ pointed out in #14...
YMMV...
TXnMA
I just checked my Surface, and all of my .mp3 files are bought and paid for, so I guess I’m okay.