In my experience, my GT will go after anything that looks like it will fit in his mouth. But, that's just my experience. My GT left large snails alone, although your JD might not.
If you add snails again in the future, I would add large ones and also watch the tank for as long as possible after putting them in. If you see him nipping at the snail(s) or looking really interested in them then they still might get eaten.
If you add snails again in the future, I would add large ones and also watch the tank for as long as possible after putting them in. If you see him nipping at the snail(s) or looking really interested in them then they still might get eaten.