The dogs you mentioned are not whom I refer to. At least, you do not get cyberdog in Navarro. You get from Dr Henry in NCR.
Who the same Dr Henry in FONV I would imagine.
Brain gone bad. So, who is it say after FO2 Dog roamed around, went Colorado, got taken by Legion, etc.
And not to mention that this dog is part of Enclave experimentation that going on a little before FO2, seeing how Dr Henry is not 150 years old, and the only cyberdog experimenta we know of are his and Big Mountain, I would put cyberdogs as a rare thing.
While it's the same Henry at Jacobstown, Rex isn't the cyberdog from 2. There's no little linking hint to be found. It's as true as the Courier being the Chosen One's son(Not true, never to be canon. But vagueness allows you to RP as an offspring/grandkid if you wish. Just as you can roleplay as anything else)
Obviously Henry helped with the brain transplant due to his knowledge of the area along with 2's K-9 which he took when he departed the Enclave.
We know Rex was a police dog from Denver who somehow got into the King's company, and through both NV and Van Buren documents we know Denver is filled with cyberdogs, meaning 2's was in no way unique and with Rex from Denver not being one from Navarro(Henry took it from Novarro before the start of 2. That cyberdog was also made by the other scientist at Novarro. It wasn't a police unit dog)Plus OWB had them as well.
And speaking of Denver, anyone know if the New Plague still persisting to 3/New Vegas's timeline is canon? On a separate but related note the pre-war Hoover Dam sabotage by Chinese agents of the U.S.'s biological weapon to use on Chinese soldiers/Enemy states is still being debated as well but with the stealth suits being there it's clear Obsidian wants it set as canon.