My family has a "99 year lease" on a property from the federal government in the US, and even though it's called that, it really just renews something like ever

My family has a "99 year lease" on a property from the federal government in the US, and even though it's called that, it really just renews something like every 20 years. Not sure if in the UK they literally count 99 years. (Edit: To be clear, it's been in the family since the 1930s, so it's gone through several renewals already.)