Maybe instead of asking a dev, are there any legacy players that managed to clear Coil in its form during 1.0 (if it existed)?

Because, if that shield existed back then, there may be no guarantee that it's coming out until they put more bosses into Coil past Twintania. Also, that might explain why it's in the database but not found yet in game.

I'm pretty sure the devs are not going to reply to this as telling us where something drops in the game might be considered a "hint".

That aside, it's kind of a puzzle. I'm sure someone will discover a answer as more content is added to the game.