A320 FLT CREW REPORTS MISSING CROSSING RESTRICTION AFTER RWY CHANGE DELETES FLT CREW ENTERED DATA.

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CLEARANCE WAS RECEIVED TO CROSS LARKS INTERSECTION AT 16000 FT AND 250 KNOTS. WE HAD PREVIOUSLY BRIEFED AND PLANNED TO CROSS AT 17000 FT PER THE PUBLISHED PROCEDURE AND ALSO BRIEFED FOR A RWY 16L ARRIVAL. WE ASSESSED THAT THE 16000 FT; 250 KNOTS RESTRICTION AT LARKS BODED A RWY 26 LANDING; BASED UPON THE ATIS AND PRIOR EXPERIENCE. WE CHANGED THE ARRIVAL RWY IN THE ACTIVE FLIGHT PLAN TO RWY 26 AND REBRIEFED THE LANDING RWY; BUT WE DID NOT REVERIFY THE CROSSING RESTRICTION WE HAD PREVIOUSLY LOADED IN THE FMGC. I INITIATED THE DESCENT BASED UPON THE CALCULATED TOD FROM THE FMGC. DESCENDING THROUGH ABOUT 32000 FT; DEN CENTER ASKED US WHAT OUR ALTITUDE WAS AND WHETHER WE WOULD COMPLY WITH OUR ASSIGNED CROSSING RESTRICTION. AT THAT POINT WE REALIZED THAT WE WERE TOO HIGH AND TOO FAST TO COMPLY BECAUSE NO ARRIVAL CONSTRAINT WAS INCLUDED IN THE ACTIVE FLIGHT PLAN DUE TO OUR LATE RUNWAY CHANGE. WE ADVISED ATC AND EXPEDITED OUR DESCENT. THERE WAS NO KNOWN TRAFFIC CONFLICT. IN THE FUTURE I WILL BE MORE DILIGENT IN CROSS-CHECKING AND VERIFYING THE VALIDITY OF THE MANAGED DESCENT INFORMATION FROM THE FMGC. I WOULD PREFER THAT THE FMGC WOULD NOT DUMP CREW-LOADED ARRIVAL CONSTRAINTS WHEN THE LANDING RUNWAY IS CHANGED.