I can't say if it's right or wrong, but in relation to your specific example, there are "adverse possession" laws that grant legal rights to the occupier of land in the US.[1]
It's the receiver, so it's more like, you're asserting your right to leave your door wide open on a street that is suddenly much more busy.
De facto possession of spectrum was heavily litigated in the early days of radio. There basically is none (not legal advice!), essentially no one has a claim on spectrum in the USA that is not assigned or regulated by the FCC. You have to sign away any claim to spectrum from before the establishment of the FCC to get a ham license or similar radiotelephone licenses. Nobody is around anymore that was operating then anyway. The language is blandly bureaucratic but in context that is what it means: "The Applicant/Licensee waives any claim to the use of any particular frequency or of the electromagnetic spectrum as against the regulatory power of the United States because of the previous use of the same, whether by license or otherwise, and requests an authorization in accordance with this application."
There is probably some similar language in the applications for other licensed bands.
De facto possession of spectrum was heavily litigated in the early days of radio. There basically is none (not legal advice!), essentially no one has a claim on spectrum in the USA that is not assigned or regulated by the FCC. You have to sign away any claim to spectrum from before the establishment of the FCC to get a ham license or similar radiotelephone licenses. Nobody is around anymore that was operating then anyway. The language is blandly bureaucratic but in context that is what it means: "The Applicant/Licensee waives any claim to the use of any particular frequency or of the electromagnetic spectrum as against the regulatory power of the United States because of the previous use of the same, whether by license or otherwise, and requests an authorization in accordance with this application."
There is probably some similar language in the applications for other licensed bands.