I am currently over a year into my clean custom neighbourhood, and it's working fine, no new townies or NPC's added without my say-so.

However! I have just installed University and am having trouble with the spawning of tonnes and tonnes of secret society members. I have nossrespawn hack to limit this, but so far it has created about 20 ss members.

Does anyone know the limit at which the game will decide that it has enough? Is there a limit at all, or will it just keep creating more and more of them?

I use Antiredundancy.
It works really well, but every so often it will randomly create a NPC that I already have.
I only have one of each NPC in my game (with the exception of 2 drivers, 3 cashiers, and 3 servers).
But recently it's created and extra Barman, Police Officer, and today an extra Repair Woman.

I know the game will still create NPC's if it absolutely needs them. I was just wondering why it would need NPC's that I already have?  

I'm trying to keep my character files below 300 (I'm at 222)

I use Notownieregen and Antiredundancy.
I have just installed Seasons and updated both hacks, but I'm still getting different Garden Club members each time I visit a different lot, and I now have 6 new sims.
I keep a tight watch on my Sims and know each and every Sim/Townie/NPC, so I can tell right away if someone is new.

Any ideas how I can stop it creating a new Garden Club Member each time it needs one?