I would guess longer than 2 years, since salt slows plant growth.
Also, this was a body buried in a plastic bag (perhaps double bagged). Plastic bags create an environment ripe for adipocere, which slows decomp. And since this body was buried AND bagged, insect activity would be minimal, imo.
Could have been there awhile I agree. Sandy could have partially uncovered it depending on how much water came over the trail there.