wouldn;t you have to give a specific version?
the bois sec / canray version is very weird
there may be 'straighter' ones out there
plus it doesn;t have a band so it;s kind of ambiguous in points what would be right
if it had a band at least you could figure out what the bass player was doing
i don;t think it goes to the IV
there is a spot where they hit one loud point and that could possibly be a B flat [VII chord]
but you can;t hit that on a C accordion anyway
the version on amazon is also about 3/4 of a semitone flat
it;s somewhere between keys of B and C