ITYM "to remember". IIRC, the last Egyptian
scribe who could read and
write the script died in the 3rd Century CE; Champollion did his work
on the Rosetta stone in the very late 18th and early 19th, so at least
1500 years--and it took another century to get some of the readings right.
But they didn't had the net, backups in DLT and replicability :)