Home Health Recert (G0179)

Pt Start of Care was 09/30/12 thru 11/28/12 and we billed the G0180 for Medicare pt. Pt have another encounter with Home Care on 12/17/12 thru 02/14/13. How do I know its a recert? Does it mean the 12/17/12 (after 60 days) is a recert (G0179)? Do I keep billing recert until the pt is done with Home Care? Thanks!