I dunno... Everything I know first hand is from when Guillermo was in the chair (I know, massively out of date), but at that point smaug was fully animatronic (jizz) and the studio was pushing for 3 movies with a 3rd acting as a bridge. This info is courtesy of (SWIM) drunk scottish guy in hellboy 2 crew fleece who hangs around metal bars in camden town