In Cartmans Mom is Still a Dirty Slut they take that last commerical about 3 minutes after the last one. This can only mean one thing: There are different endings. There have to be different endings so no onw would know which one was the real one. The same thing happened if you remember in the Simpsons edisode Who Shot Mr. Burns? When you watch the Simpsons 138th epsiode Spectactular they say that they did this and they show you the alternate endings.
The same thing must have happened to CMSDS