HOWEVER, BUT, and NEVERTHELESS...
Do not get careless and start toting your expired FMM around from a prior trip.
Immigration is allowed to seize the expired FMM and assign a multa up to a thousand pesos which you will pay at a bank. Sounds humorous until it happens. I happened to be at the Sonoyta INM office when this happened and the man got angry and cursed out the immigration officer. The guy photocopied the expired FMM, stapled it to the wall, turn the man and DW around and they were forced to head the other way. I politely asked the officer what was going to happen. He replied that the hothead is "not going to get an FMM at this office".