Your conclusion is illogical. The only conclusion you could possibly make is that the rig and Navarro were the only LOCAL bases. Canon is never exclusive. Unless canon explicitly states something, anything not covered by canon is possible. Nothing in your above statements preclude Enclave installations elsewhere.
Only the fact that the FEV in Fallout 2 would have had a
global effect, and not a local one like in Fallout 3. If there were other production facilities outside of the Oil Rig Richardson certainly would have considered the staff a priority for inoculation. There's nothing illogical about coming to a conclusion based on the facts presented in a final product.
You can speculate on what happened
after Fallout 2, but during Fallout 2 there is absolutely no indication that they have any factories outside of the oil rig.