I can't remember exactly, but I think I read it off a Japanese TF board about 10 years (Naito Naonori's Transformers Net??? Can't remember (either way that board has been defunct for years now)...
Anyway, TFwiki only says that it's rumoured as a lost mould... but the fact that TOMY have reissued Encore Devastator now should disprove that rumour - because Takara/TOMY have never reissued a toy from a completely lost/destroyed/damaged mould before. The most extensively damaged mould that had to be repaired for a reissue was Optimus Prime -- it's obvious from the reissue's body that it was cast from G2 Optimus Prime and not G1, but even Takara admitted that the moulds for the arms had been destroyed/lost and they had to spend truckloads (sic) of money to build new moulds for Convoy's arms. Takara said that it was a big expensive for them but they figured that it must have been worth it because Convoy/Optimus Prime is arguably the single most popular/iconic character in the TF franchise. And we've certainly seen HasTak milk that mould something chronic -- it would have to be the single most reissued Transformer toy out there!
I'd say that the existence of Encore Devastator probably disproves any theory/rumour that Takara had ever lost the Devastator mould. They may have lost parts of it -- like maybe the moulds for Scavenger's legs/feet?? But that would surprise me, considering how much Takara harped on about how much they shelled out to reconstruct Optimus Prime's arms, I'm surprised TOMY hasn't said boo about the cost of reconstructing the Constructicons. So odds are the mould was never lost ... at least not entirely.