double frame numbers
Just means some are from uplink and some from downlink frequencies. Some subchannels of SDCCH have uplink and downlink on the same frame and if the target phone is clone enough you can receive the frames from the phone as well. The 'arfcn' field should have the ARFCN_UPLINK flag set (grep libosmocore to know the value).
Cheers,
Sylvain