Exactly what I was thinking.
But, I am betting that it doesn’t apply to the government.
“Adverse occupancy” also applies to government land.
And of course, there was always the concept of “homesteading” and “proving up the land”. Much of the West was settled in just this way.
But territory once occupied by the nation that used to be known as “the United States of America” might no longer be subject to this old established tenet of English common law.