VIA listening to San Juan center the area north is using 13297 as primary and 11330 as backup. CHEERS
I know it can change but it seems like for quite awhile now NY have been using 11330 and 6577 as backup frequencies only, resulting in very little traffic on them. Whereas 5520 and 5550 have been the main primary frequencies in the evenings (they usually take over from 8825 and 8846 as conditions warrant).
On average you will hear much more traffic on 5520/5550 than you will on 6577/11330. Ideally it would be great if all frequencies could be covered but with limited radios available it just seems like a better use of resources to monitor the most active primary frequencies.