A qualifier does not always identify a new individual or introduce independent information. Sometimes it reinforces a meaning already implicit in the modified term.
أَمْسِ الدَّابِرُ كَانَ يَوْمًا عَظِيمًا
Yesterday, now gone, was a momentous day.
«أمس» already refers to yesterday, while «الدابر» stresses something that has passed away. The adjective does not select a second yesterday; its force is to reinforce the sense of passing.