aztruck - I do a lot of work with the FAA office in Orlando.
I did a "search" of FAA DPE's (designated pilot examiners) about twelve months ago when the question came up on ppriune before.
The guys in the office tell me that the DPE authorisation IS geographic - if you are an Orlando DPE you cannot test in Miami, etc. etc.
Each examiner has the right to REQUEST a special authorisation from Oklahoma to do "external testing".
When I mentioned that I had been, personally, to an FAA DPE in Frankfurt many years ago, I was told that "under the previous regime, DPE's were based all around the globe - but the current man in charge is not replacing any DPE from outside the USA - if he is still there, he can continue - if he retires, the place is lost.
I think Frankfurt still has a DPE - but the UK does not.