Adhan for a missed prayer remains relevant because the obligation to perform that prayer remains, despite its time having passed.
In a continuous session of multiple make-up prayers, the first adhan serves the general announcement, while each prayer is individually introduced by iqamah. That explains the option of iqamah alone for later prayers.
This is not the same issue as introducing separate adhans for Eid, funeral or Friday prayers.
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Bab al-Adhan: The Adhan, Iqamah and Juristic Rulings
Adhan for a missed prayer remains relevant because the obligation to perform that prayer remains, despite its time having passed.
In a continuous session of multiple make-up prayers, the first adhan serves the general announcement, while each prayer is individually introduced by iqamah. That explains the option of iqamah alone for later prayers.
This is not the same issue as introducing separate adhans for Eid, funeral or Friday prayers.