More is dependent on if they've laid eggs or if there are more hidden in the tank that you can't see. In my previous planted days, I had major issues with them several times. I've seen them go as far as burrowing into the gravel a bit and laying their eggs in there. From my experiences, here's my suggestion:
Keep your eyes out for the eggs. If you can find any, remove them. They're small, white and in a cloud (little group). Stray from using had-a-snail or any of those type products as they are a bad idea for your tank (copper solutions), just keep your eyes open and manually eradicate any you can find. Some suggest making traps with film canisters (google it) but this has never worked for me.
If you have a large tank and start having snail population issues, you could get clown loaches. Clown loaches love snails! Just understand they grow to be pretty big so it's really only applicable for a large tank.
-HSFT