The sulawesi nerites (horned, tiger, zebra) are all pretty sensitive, and they've had a long journey from indonesia to the store, then from the store to your house, going through several shocking parameter changes. It's not surprising to me that some die.
That said, nerites are notorious for hibernating every time they're transferred to different parameters or temperatures. I've gotten a package of 20 nerites before, and I had thought most of them were dead when I got them. Much to my surprise, they all started waking up, slowly at first.. Moving maybe an inch or two during the day. But most of them came around... I suggest doing the sniff test. If they smell like death (it's a STRONG smell), throw them out. If you pick one up and smell it, and there's no death smell, it's fine, just adjusting.
The smell test is the only way you can know for sure if they're dead or not.