Recently, on flightradar24, I noticed an image that looked like two overlapping aircraft on a northerly heading near the SC coast. The image attracted my attention when it continued to appear to be two aircraft overlapping for some time. The flightradar24 data indicated both were the exact same model aircraft (Cessna 210), but with different N-numbers. The N-numbers for each aircraft were similar except for two digits being reversed. Their serial numbers were completely different. Looking up the N-numbers in the FAA Registry, both came back as invalid. Looking up the serial numbers in the FAA Registry, the same aircraft model came back for both, with the two N-numbers as shown in flightradar24 data, but with different owners. I was reluctant to post this because I have let the N-numbers and serial numbers get away from me, but curiosity got the better of me. Any ideas?