Retracing lost exploration data

I recently had a lithobraking incident when I misjudged the new-to-me Caspian deeper atmospheric entry. I'm retracing my steps from EDSM, and I notice that as I return to these systems, they are already FSS'd. No waveforms on the slider, just bodies that have been ID'd. Do I need to re-FSS them anyway to get credit/data? Is honking enough? Is revisiting the system enough?