The Exotic Ciphers are required to purchase any exotic from the monument to lost light along with other materials. You only need spoils of conquest for older raid specific exotic weapons (and the Always on Time sparrow). The Forsaken ciphers you dismantled were for Forsaken Exotics only, I doubt Bungie will undo your dismantling as its a player error. We have all dismantled something important from time to time.
Edited by Pastor of Muppets: 12/7/2021 9:02:25 PMI did the same thing, caught myself on the last cypher. Mistakenly thinking I was collecting shards not exchanging them for cyphers. Oh well, only 1 exotic from the kiosk I need, will just have to use the Xur cypher quest to get it. ( I agree though, my lack of noticing it was aggravating)