Ada' concerns carrying out the original obligation in its prescribed form. Qada' concerns fulfilling a missed or replacement obligation. Both may have complete and deficient forms in the legal analysis.
In questions of prayer timing, purity for circumambulation, remedy for mistakes or return of property, one cannot stop at “something was done.” One must ask which requirements were satisfied and whether the remaining defect admits a legally recognized remedy.
Replacing fungible property with its equivalent is not the same as paying the assessed value of non-fungible property. Some deficiencies cannot be settled by any convenient substitute.
Analyze the original duty, its time and subject, the exact deficiency and the authorized form of compensation.