I suspect you're seeing hitchhiking snails that you didn't realize you had rather than babies of any of the snails you know about.
There are some big obstacles to "margarita" snails breeding in a reef tank. The two biggest ones are their delicate larval stage and the extreme temperature. Margarita snails are from cold water. It's hard enough getting their close, tropical relatives to breed in reef tanks.
If these were babies from the spawning event the original poster saw, they certainly wouldn't be this big within a couple of weeks.