This last issues of the mini-series might as well have been entitled "A Tale of Two Sentries."
Because, at the end, the Watcher of Earth-99126 (hereafter known as "Earth-Z") soliloquizes how sending the Sentry of this world back into the recent past of Earth-2149 will create a causality loop that will hopefully keep the zombie virus from spreading any further. Of course, we all know that hope was ultimately dashed! What with the Marvel Zombies of Earth-2149 eventually invading Earth-8101 (hereafter known as "Marvel Ape Earth") and thereby leading to the creation of two more divergent realities (Earth-21050 and Earth-95019)!
But, one question has remained unanswered despite all the sequel mini-series done since. Where did the other Sentry come from?!
Let's look at the facts. In the original min-series about the Marvel Zombies, it was revealed by the Magneto of Earth-2149 that the zombified super-being, known as the Sentry, first materialized aboard his extra-terrestrial outpost, Asteroid M. And that he (Magneto) sent him to Earth to decimate the mutant-hating humans. Only for things to get out of hand almost immediately.
Yet, in the sequel mini-series "Marvel Zombies vs. the Army of Darkness" (co-published by Dynamite Entertainment), the zombified Sentry had first materialized outside the "Pearly Gates" alongside Ash Williams the Deadite Slayer! So, which one was from Earth-Z?
Personally, I think it was the one that first met Magneto. The other one (the one that Ash accidentally brought to Earth-Z from the "Pearly Gates") was most likely from yet another Marvel Earth! More specifically; Earth-8212. The home of Reed Richards' Rocket Group!
Super-powerless analog of the Fantastic Four.
This is how I picture it. Earth-8212 is invaded the Four Horsemen of the Axi-Tun. It takes the combined might of the Rocket Group and Dr. Stephen Strange to subdue the Horsemen called War and Death. While Famine and Pestilence get a Pyrrhic victory over the local version of the Sentry by hitting him with their own combined powers, just micro-seconds before he clobbers them!
Soon realizing there is no cure, medical or mystical, for what he is slowly becoming, the Sentry agrees to sacrifice himself by exiling himself to the Negative Zone via an experimental teleportation device recently invented by Richards. Upon arriving there, however, he gets attacked by Annihilus and his cosmic control rod. The ensuing battle is fierce, but brief. With Annihilus getting destroyed, once and for all, using the energies of the rod. Unfortunately, those same energies teleport the Sentry to an area of Limbo that serves as a boundary marker between Immortus' version...and the version ruled by Belasco (or one of his successors)!
This is the Sentry who winds up on Earth-Z alongside Ash Williams. Well, that's my theory and I'm sticking to it!