AN UNVERIFIED XPONDER CHANGE IS NOT FOLLOWED-UP BY SBN DEP CTL WHICH RESULTS IN AN OPDEV AND OPERROR.

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ACFT X DEPARTED SBN FOR ATL. ALL RADAR POS COMBINED. APPROX 12 ACFT ON FREQ. ACFT X DEPARTED ON A 1200 CODE RATHER THAN ASSIGNED CODE. ACFT X WAS RADAR IDENTED; CLBED TO 8000 FT; AND TURNED ON COURSE. ACFT X LEVELED AT 8000 FT AFTER PASSING 900 FT BELOW AN OVERFLT AT 8000 FT AND APPROX 2 MI HORIZLY. ACFT X ENTERED FWA AIRSPACE AT 8000 FT ON A 1200 CODE WITHOUT A HDOF. ACFT X REQUESTED HIGHER AND I INSTRUCTED HIM TO IDENT. I OBSERVED A 1200 CODE TARGET IDENTING IN FWA AIRSPACE AND ASKED IF ACFT X WAS ON HIS ASSIGNED CODE. HE ADMITTED TO BEING ON THE WRONG CODE AND MADE THE CHANGE. COORD WITH FWA; APCH WAS ACCOMPLISHED TO 'ISSUE' THE ACFT AT 8000 FT AN IFR CLRNC AND CLB TO CTR ALTS. ERROR: 1) I VIOLATED FWA AIRSPACE. 2) I ALLOWED ACFT X TO PASS WITHIN 900 FT OF OVERFLT TFC. 3) I DID NOT ENSURE DEPARTING ACFT WAS ON THE PROPER CODE. 4) THE LCL CTLR FAILED TO CALL THE 'NO TAG' VIA LAND LINES. CONTRIBUTING FACTORS: 1) ACFT X DID NOT PROPERLY ADJUST THE XPONDER CODE. 2) THE LCL CTLR DID NOT NOTIFY RADAR OF THE 'NO TAG' IN ACCORDANCE WITH LCL SBN ORDERS. 3) RADAR POS CONTINUED TO BE COMBINED IN SPITE OF INCREASE TFC LOADS. 4) RADAR CTLR DID NOT ENSURE DATA TAG ACQUISITION. CORRECTIVE ACTIONS: 1) DO NOT TURN DEPS UNTIL DATA TAG ACQUISITION TO PROMOTE PLT CALL. 2) REMIND LCL CTLR TO CALL 'NO TAGS' TO TRACON. 3) ENCOURAGE THE DECOMBINING OF POS AS TFC INCREASES. 4) HOPE THAT PLTS WILL PROPERLY ADJUST EQUIP PRIOR TO FLT.