Titans didn't always have the full die. 780 Ti had the full die before they then release the Titan Black for example.
OG Titan: GK110, 2688 cores, 6GB, released 2/21/13
GTX 780 Ti: GK110, 2880 cores, 3GB, released 11/7/13
Titan Black: GK110, 2880 cores, 6GB, release 2/18/14
This goes back to "Titan class" is an extremely loose term with a sliding scale of what it means generation to generation.
I always considered the 3090, 4090 a rebrand and pricehike of the 80 Ti tier first before I ever considered them Titans. The only thing I can say that makes them quasi able to occupy both product tiers now is the choice of drivers and the larger VRAM capacity, and continued use of the flagship die. But as we have seen Titans historically have not always used fully unlocked dies either.