It has been widely acknowledged in the dungeon-running community that several dungeon recipes no longer drop:
-Recipe: Vallog's Demise (from Vallog, CM P3)
-Recipe: The Replicator (from Tazza? SE P1)
-Recipe: Shukov's Launch Codes (from endboss SE P3)
-Recipe: Ring of Blood (from Givna the Butcher, HotW P1)
-Recipe: Alpha Conduit (from Subject Alpha, CoE P?)
-Recipe: Stargazer's Pendant (from Jotun Stargazer, Arah P1)
This list is based on the absence of seeing these as drops, the replacement of the recipes with their crafted item, and the anomalously low unlock-rates on GW2 Efficiency.
Last night, I messaged GW2 Support, who confirmed that these recipes are bugged, and no longer drop. Since these have disappeared since 2013, can this bug please be fixed.