I have been assuming that to renew (extend) your retirement visa that you must do this in the province (in this case CM) that you reside in. Yet I have heard of two people this week that claimed that they had gone down to Pattaya and successfully got their one year extension. Is this possible? (A comment from UbonJoe would really be appreciated!)

The rules state you must apply for the extension where you are living. To apply for one in a different province you have to formally change your address to that province and at many offices that requires some form of proof of residence.

I suspect the 2 people you mentioned used an agent to do the extensions in Pattaya.

Usually you need to move to an area to use that office. The people who went down to pattaya would have been using an agent so all the normal rules go out the window. They will possibly have problems if they ever try to continue using their local immigration unless the formally move back there like a new arrival, tm28, tm30 1st tm47 etc.