I know they can’t be permanent because of the rule against perpetuities[1], but since this was in 99 I don’t think that applies.

IMO the non permanent nature of these sorts of grants is a good thing because if we don’t have limitations then we’ll eventually end up in a necrocacy where the long dead have more say over how property and the government is managed than the living.

[1] https://en.wikipedia.org/wiki/Rule_against_perpetuities