Those are quite different lengths in practice. 99 is less than some individual humans have lived. 999 is longer than any* country has continuously lived.
If I have a 999 year leasehold, that's the same as ownership in practical terms as my ownership goes away when the government fails and is replaced/taken over/overthrown.
In tech specifically, a 99 year lease is practically permanent as well. (1925 was before the first RF transmission of a television picture.)
Contenders: Denmark, Hungary, China, Czechia, France, England and a bunch of others depending on how you count, like Georgia, Russia, Ukraine, Sweden etc.