Lifetime is just "numbers of bytes written"/"expected lifetime bytes written"
There's a separate SMART attribute for remaining spare, and that is supposed to stay at 100% until you reach 100% lifetime, but the actual failure of cells can come sooner or later.
The scary conclusion I came to is based on the assumption of "expected lifetime bytes written" being proportional to SSD size (i.e. based on fixed Flash erase counts, which is usually how it goes); for the worst example we have so have, scaling his 3% from 2T to 256GB machines would mean some of those could be reaching 100% before the first year is up.
