The hypothesis of a reign more than three decades long for Nyuserre Ini is supported, albeit indirectly, by reliefs discovered in his solar temple showing him participating in a Sed festival.
This festival was meant to rejuvenate the king and was normally first celebrated after 30 years of rule.
Representations of the festival were part of the typical decorations of temples associated to the king during the Old Kingdom and mere depictions of it do not necessarily imply a long reign.
For example, a relief showing Sahure in the tunic of the Sed festival has been found in his mortuary temple, although both historical sources and archeological evidence agree that he ruled Egypt for less than 14 full years.

Yet, in Nyuserre's case, these reliefs taken together with the archaeological evidence have convinced most Egyptologists that Nyuserre enjoyed over 30 years of reign and that "the sed-festival scenes from Abu Gurab [most probably reflect] the 30th jubilee of the king's accession to the throne".

The reliefs of Nyuserre's Sed festival offer a rare glimpse into the ritual acts carried out during this ceremony.
In particular, the festival seems to have involved a procession in a barque over a body of water, a detail either not represented or lost in all subsequent representations of the festival until the reign of Amenhotep III (fl.
c. 1390–1350 BCE), over 1000 years after Nyuserre's lifetime.
The hypothesis of a reign more than three decades long for Nyuserre Ini is supported, albeit indirectly, by reliefs discovered in his solar temple showing him participating in a Sed festival. This festival was meant to rejuvenate the king and was normally first celebrated after 30 years of rule. Representations of the festival were part of the typical decorations of temples associated to the king during the Old Kingdom and mere depictions of it do not necessarily imply a long reign. For example, a relief showing Sahure in the tunic of the Sed festival has been found in his mortuary temple, although both historical sources and archeological evidence agree that he ruled Egypt for less than 14 full years.
Yet, in Nyuserre's case, these reliefs taken together with the archaeological evidence have convinced most Egyptologists that Nyuserre enjoyed over 30 years of reign and that "the sed-festival scenes from Abu Gurab [most probably reflect] the 30th jubilee of the king's accession to the throne".
The reliefs of Nyuserre's Sed festival offer a rare glimpse into the ritual acts carried out during this ceremony. In particular, the festival seems to have involved a procession in a barque over a body of water, a detail either not represented or lost in all subsequent representations of the festival until the reign of Amenhotep III (fl. c. 1390–1350 BCE), over 1000 years after Nyuserre's lifetime.
Nyuserre Ini