The 1620 was the older style hull. The "pocket" was bigger and the bow rounder.
Some 1620's had the flip seat, but most did not.
The 1622 is the current production model.
Both are well made and perform great w/ 90 HP.
I like the 1620, because I was never a fan of the flip seat.
(Too low with no leg room when used, so always left it closed & sat on top)
The 1620 used the "folding seat" space for storage, always needed on a small boat.
Both hulls ride good, pole good, and are easy to walk around.