I believe Garmin's "lifetime" update is the "lifetime" of the unit. It is not forever. I have 2 Garmin's that still work, but upgrades are no longer available.
From Garmin's website:
"... if your Garmin product comes bundled with a nüMaps Lifetime or other lifetime map subscription, you will receive map data updates when and as such updates are made available on Garmin.com during the useful life of 1 compatible Garmin product or as long as Garmin receives map data from a third party supplier, whichever is shorter. ..."