I followed most of your directions
I had a 2.5 gal tank with FW but nothing on the bottom, no driftwood, no flat anything, except the bottom of the tank (no substrate). I was placing Cory eggs in there to hatch out when ready. I had the moss/algae and a few plants floating around. Because the Corys are so tiny, I wanted to be able to see them with a magnifying glass when they hatched, which happened over a period of weeks...
Meanwhile I put the snail in there to clean up the unhatched eggs and debris. The snail did a good job, and all of a sudden I realized there were more snails than just the one I started with. Now I had no snails before that, not even hidden on plants. I used my own plants, at first. I checked all over the tank, and the only place the eggs were was on a piece of Hornwort. No question that was the eggs. Now the Hornwort had been with me for 6 months... so no eggs came in with it when I put it in the catfish tank. The snail did lay her eggs, and they hatched. So there are variables in any tank, and this was my own. I gave the snail no real place to lay her eggs, so she picked the only thing available. Because of the moss on portions of the bottom if she laid eggs there, that was also possible.
I did everything else, had a slight bubbler, had algae, had baby cats, and nothing beyond. I really was trying to hatch some Corys, not snails. But conditions told the snail, this is a good place for you to lay your eggs. So she did. And because it got hot lately, the snails bloomed into many, can't even count them. Their shells look firm and solid, they seem to be in fine shape. For every normal event, there are others that one doesn't plan on... I will keep them vitalized with calcium and minerals, and feed them plenty of algae, shrimp, and such.
Last thing, these were sold as Nerites, is it possible that they are NOT, and are a different type of snail -- not Ramshorn -- but I can say that they match the pix of Nerites, even the brown zebra look to them, and they are a smaller size of snail.