Any ideas as to why Nepeta's aspect's symbol wasn't incorporated into Davpetasprite^2's symbol?

Because a squared sprite is linked to every doomed iteraction of its components and while there have been at least one doomed Dave to god tier, it appears that no Nepeta has ever ascended. I just went and scanned through Ministrife and the army page to make sure and we have not seen one god tier Nepeta in canon.