Well the exotic engram description is an engram with a predestined outcome. Contains a new exotic if any remain to be collected; otherwise, it contains a random piece of exotic armor. And well I am missing lots of exotics from all seasons so I was hoping for any of them.
Looking at your collection, every exotic weapon you're still missing is either a quest exotic, a raid exotic, or one that's available through the new kiosk (or will be in coming seasons). For exotic armor, you already have everything on your warlock that can possibly come from engrams, and you can't get exotic armor for classes other than the one you're using at that moment, so in the future, if you buy engrams/use ciphers from Xur, make sure you do it on your hunter or your titan, because your warlock will only ever get duplicates.