To the best of my knowledge neither can be legally extended. Do you have a link? Or remember where you saw that info? Would sure help a lot of people.
UPDATE: I did a Google on this subject. You have to read the results carefully. The info that popped up referred to people with RT or RP that were renewing the visa and needed to renew the TIP. NOT for those with an FMM. The articles I found on renewing an FMM was for those with a 30,60 or 90 day permit. These can be extended to the 180 Max. The article stated that no FMM can be extended beyond 180 days without leaving the country. BTW If your TIP has expired you can get a permit that allows you to legally drive to the border. Years ago you could get an FMT extended with some Mordida. Things have changed.
Moisheh
