Astrea snail baby question

[Chuja's reef]

So my snail recently layed eggs and now I'm seeing little baby snails, i was wondering how often it is that they survive to become fully grown

 

[Ocelaris]

I don't know about astrea snails, but my trochus laid eggs, had hundreds of baby snails, and today (about 2 years into this tank) I have probably about a hundred? No idea, there are way too many to count. They seem to be self limiting, haven't seen many babies, but there are always hordes of them roaming the tank doing their job (and they're great at it!)