يَوْمَئِذٍ تُحَدِّثُ أَخْبَارَهَا
On that Day the earth will report its accounts. (99:4)
إِنَّ رَبَّهُمْ بِهِمْ يَوْمَئِذٍ لَخَبِيرٌ
Indeed their Lord will be fully aware of them on that Day. (100:11)
Both verses employ yawmāʾidhin, but the first pictures the earth reporting, whereas the second emphatically asserts divine knowledge. In one, the imperfect verb lends vividness to a future scene; in the other, inna and the lām reinforce a predicative relation.
Sharing a word does not make two verses rhetorically identical. Sound analysis first identifies syntax, then the contextual aim, and finally the effect achieved by that structure.