Where are you getting that from?
Westchester's 700 MHz frequencies all have a construction deadline of November 2023. The county was granted an extension last year for all licenses, none of which have expired.
Oh and those frequencies weren't purchased; every county in the state was allocated X amount of 700 MHz spectrum years ago by the Regional Planning Committee (Region 8 in this case). Whether or not the counties accepted that spectrum or subsequently applied for additional spectrum was left to them to decide. Coordination of the 700 MHz general pool (SY) frequencies is solely the responsibility of Region 8, not a traditional frequency coordinator, and so there are no fees involved for the licensing.