I've only seen partial areas on slugs like that before in the flesh. Must be quite an advanced stage of calcification, I think Stefan had a whole batch of this with his tetrataenia female? It's good they're coming easy with gentle persuasion.
I had a partial calcification at the head of a blockage of two fused ovae my Florida blue had to expel this year. I played the waiting game with her and she cleared it much the same - starting contractions after handling that included some exploratory squeezing.