jjDrawSprite, for better or worse, doesn't take the initiative to load sprites from anims.j2a if they haven't already been loaded for that level. To remedy this, either place a corresponding object or ambient sound event somewhere in JCS, or else call jjOBJ::determineCurAnim, which does try to load missing sprites.

(Please hold any concerns about that a) not making sense or b) not being documented, because you're right. There wasn't time/understanding to put in place a more elaborate/appropriate API for such things, but there needed to be some way of loading sprites in the meantime, so determineCurAnim got to be an interim solution)