https://www.polygon.com/2018/8/3/17646592/bungie-destiny-2-exotics-collection-pre-patch-forsaken

One of Destiny 2: Forsaken’s biggest features is the new Collections tab, which will let players track and re-acquire weapons or armor that they’ve gotten over the past year. In anticipation of this new change, the current collection tab attached to it will be disabled one week before Forsaken’s launch.

Compared to what we’ve seen of Forsaken’s Collections tab, the current offering is very limited. Players can currently re-acquire any exotic weapons or armor that they’ve already collected in Destiny 2, even if they’ve deleted them before. Player emblems are also stored here.