I have a 2720 gps with garmin lifetime map update since 2009 and have no problem updating. just make sure to delete your garmin registration with Garmin so that the new owner can register it and be able to get software update and purchase map updates.
I think the confusion (on my part) is that the more recent maps from Garmin are designated "NT" and my SP 2610 can't use those and I lumped the 2600 and 2700 series Street Pilots together. It appears the 2720 can use the NT maps. Sorry for the misinformation.