When an untimed duty is fulfilled later, its fulfillment is still called Ada in this classification: the outstanding duty is being performed, rather than a prescribed performance window having expired and a new Qada duty replacing it.
For example, paying outstanding Zakat later still fulfills the Zakat duty. Calling that payment Ada does not mean that delaying it without an excuse was permissible.
Likewise, the name “Ramadan Qada fast” remains correct. It identifies the missed Ramadan fast being made up. Fulfilling that outstanding, untimed duty does not mean that the original fast was kept during Ramadan.
The classification of performance and the permissibility of delay are different questions.
- Later Performance and the Word Ada