It's new production on each of the retired seasonal brew going into the folly packs. NB rotates in new seasonals every two years. It's not an indecision thing, it's an intentional way of introducing change into their regular lineup without disturbing their core products. I'm not sure how long they are going to continue producing the folly packs with bottles of the retired seasonals but that is the plan for now.
FWIW I thought 2 Below was the best winter seasonal and wish they would keep it as a regular winter offering, too.