I think, not sure, that is referred to as "light mussette" tuning. That is not uncommon in Canadian melodeons. A standard wet tuned accordion would have one of the mid rows tunes at A440.
That would be 15 cents difference between the mid rows, but it would sound a little different than an accordion tuned 15 cents wet, because the L and H rows aren't 15 cents off of either M row. Slightly different sound. Could be changed fairly easily.
I think that is Marc's tuning for Quebecois music, if so the 3rds and 7ths probably aren't flattened.