More likely the Enclave found that facility and refurbished it years earlier, probably before the events in FO2. Then, when the old timers went there, they knew exactly where they were going, and not relying on hope and a prayer.
I'm sure there are many such facilities around the west, possibly some larger than others.
This is exactly what the BoS did in tactics. Why would the Enclave be any different?
The BoS in Fallout Tactics came across pre-war bunkers and used them. It is also what the BoS do in all Fallout games. They go out and find pre-war bases and use them. I have a feeling that is what the Enclave remnants did. Sure it is possible they went out, found it and got it working long ago but I bet they simply came across it. Those old timers still know what they are doing when it comes to tech, they could have fixed it up.
Pre-War American tech and Pre-War Enclave tech I am guessing would be very simpler, only the Enlcave tech would be about 164 years more advanced.
There is a difference from small little bunkers in the desert and large Navarro size bases. If such an Enclave purpose built base was around they would have gone to that, not some small bunker in the Mojave.
I am not against coming across pre-war American tech or even some abandoned Enclave bunkers that were used by the Enclave on their way to DC. I am not against coming across more bunkers or pre-war military based used by Enclave Remnants, just as long as they are ex-Enclave doing their own thing.