I do believe the females can store many rounds of sperm.I thought assassins needed a M/F pair to have babies, unlike some other snails which only need 2 snails or other snails that don't need anyone. lol.
It'd be cool if you could breed them as for snails, they're pretty expensive.I got the assassin from a pet store that had many of them in there. At first I thought they were MTS that must have come in on a plant. In looking at the biggest one (which is still fairly small) I am fairly certain it is a baby assassin. Like you said time will tell.