A SINGLE ENGINE PILOT REPORTS A NMAC AT GNV WITH TRAFFIC THAT HE FAILED TO IDENTIFY AS ATC ASSIGNED PRECEDING TRAFFIC BECAUSE HE THOUGHT ATC IDENTIFIED THIRD AIRCRAFT ON SHORT FINAL WAS NUMBER ONE AND HE WAS THEREFORE NUMBER TWO.

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I APCHED GNV FROM THE S; CONTACTED TWR 15 NM OUT AND WAS ASKED TO RPT L BASE FOR RWY 29. ABOUT 7 NM L BASE TWR ASKS ME TO FOLLOW TFC AHEAD; WHICH I RPT HAVING IN SIGHT. UNKNOWN TO ME AT THE TIME; THE TFC I HAVE IN SIGHT AND START TO ENSURE PROPER SEPARATION FROM IS NOT THE PLANE TWR INTENDED ME TO FOLLOW (THE INTENDED TFC WAS FURTHER TO THE E). I CONTINUED TO FLY L BASE; KEEPING THE TFC AHEAD IN MY SCAN; AND HEAR TWR CLR A PLANE TO LAND AS #1 AND THEN CLRS ME TO LAND AS #2. SINCE THE PLANE AHEAD OF ME IS NOW ON SHORT FINAL; AND TWR JUST TOLD ME THAT I AM #2; I ASSUME THAT EVERYTHING IS IN ORDER. JUST ABOUT AS I AM PREPARING TO TURN FINAL THE PLANE ON SHORT FINAL EXECUTES A MISSED APCH; AND I START HAVING SOME MISGIVINGS. TWR RADIOS ME TO RECONFIRM THAT I AM FOLLOWING THE TFC ON FINAL; AND I RPT THAT I WAS FOLLOWING THE TFC THAT JUST WENT MISSED. TWR INFORMS ME THAT I AM FOLLOWING THE WRONG TFC; I IMMEDIATELY CLB AND DROP MY R WING TO TRY TO SPOT THE OTHER TFC. AS I BANK I SEE THE CONFLICTING TFC PASS BELOW ME; DISTANCE UNKNOWN BUT UNCOMFORTABLY CLOSE. THE CONFLICTING TFC RPTS TO TWR THAT HE JUST HAD A PLANE PASS ABOVE HIM. TWR CONFIRMS IT WAS ME AND WE HAVE A BRIEF EXCHANGE ABOUT THE IMPORTANCE OF FOLLOWING THE PROPER TFC. TWR CLRS ME TO LAND AGAIN AND I HAVE AN UNEVENTFUL LNDG. CONTRIBUTING FACTORS: 1) I DON'T RECALL TWR STATING THAT THERE WOULD BE 2 PLANES AHEAD OF ME WHEN REQUESTING THAT I FOLLOW TFC. SINCE I ALREADY HAD 1 PLANE IN SIGHT BEFORE RECEIVING THE REQUEST; I THEREFORE FOCUSED ON TRACKING IT AND LIKELY REDUCED MY SCAN. 2) WHEN ISSUING MY LNDG CLRNC; IF TWR WOULD HAVE RPTED THAT I WAS #2 TO LAND BUT #3 ON THE APCH; I WOULD HAVE DISCOVERED MY ERROR MUCH SOONER. 3) MY AIRPLANE'S TAS SYS (L3 SKYWATCH) NEVER SHOWED THE CONFLICTING TFC; SO EITHER IT WAS IN A BLIND SPOT OR HAD AN INACTIVE TRANSPONDER. CONCLUSION: NEVER STOP KEEPING YOUR SCAN UP; AND QUESTION TWR ON THE NUMBER ON PLANES AHEAD IN THE PATTERN IF NOT ANNOUNCED.