I think it might have just been left over from when I was planning to do a nipple toggle. Originally I was going to add nipples as their own object like the rat, cow, giraffe. However I just really didn't like nipples on the little sheep/goat and didn't think they would be worthwhile if they looked bad. I realised that people could probably paint little nipples on the texture, and that looked best, however that was before I added the breasts in.
Basically, nothing is locked, just unfinished/cancelled nipples