According to a contact at the BOP central office all BOP facilities are now trunked. The three 170 freqs listed are assigend nation wide as SORT (Special Operations Responce Teams) 1,2,3 until the Marshall service reclaims them or they are reallocated by NTIA.
Some facilities are still analog trunking. They will began to be upgraded to digital now that all facilities are trunked. Or so I was told.