[L4D2] Common limits don't work in finales
 

c5m5 as example, setting z_common_limit to 1 doesn't limit commons to 1, there's still like 15 of them at once

Re: [L4D2] Common limits don't work in finales
 

That is managed by the director. If you want to change the values of the director, you have to edit the scripts or use a specific plugin for that.

Re: [L4D2] Common limits don't work in finales
 

Like @Toranks said, z_common_limit works but when a director vscript (.nut files) is called, is replaced by the vscript settings.

Just as an example, you may have this bug on c6m3_port map.

The vscript (c6m3_port.nut) calls that function:

So your cvar is overridden by these settings.

You can use Left 4 Dhooks Direct to override these settings as well with L4D2_GetScriptValueInt

Just do a google search with that text you may found some examples.

This plugin used to work in the past, don't know nowadays tho:
[L4D2] VScript Director Options Unlocker

Re: [L4D2] Common limits don't work in finales
 

Re: [L4D2] Common limits don't work in finales
 

Changing the VScript value "CommonLimit" had no effect and only reduced the number slightly, still more than 1 was spawning for example when z_common_limit was set to 1. So I've written a simple plugin to completely fix over spawning: Common Limiter

Re: [L4D2] Common limits don't work in finales
 

Actually, Dragokas already did a similar plugin

[L4D1 & L4D2] Zombie limits

I'm not certain but I believe CommonLimit is not the only variable that VScripts overwrites, still has other values like MobMinSize, MobMaxSize that may change the common size