Maybe I found a way to pinpoint zstd level. After you scan with 'verbose' you can see there are several levels same. However, using ':l17' to ':l22'(without 'verbose') separately further reveal which level is real. Only with l19 it shows this:
foundzstdlevel.png
All other levels remain '0/1' even if they show same repacked size in '--verbose' scan. After this it's only matter of figuring out lib version. In this case versions working were 114, 120, 130 and 131. Probably on bigger files time would start showing difference, but I have seen these giving same result before(but also not always) so once they match, any of them should be safe.