Salvaging an eternal should unlock its entry.
For instance, say a player has an eternal crystalline helm they found before patch 3.0, if they salvage it I’m recommending the game runs a check during its destruction to see if its legendex entry is unlocked. If there’s a plan to implement trading amongst players in the future this would obviously be a bad recommendation.
Of course once you loot Legend of Eternal you already unlock the Entry on Codex.
Sorry I meant in instances where you might have a few which were found before patch 3.0.
If you already find them before 3.0 and they are already registered, the answer is yes. But if you find them before 3.0 and you do download/upload, some legends you find in legendEx may lost so you need to find them again in 3.0