Peter wrote (#09):
Qalupalik has the most brilliant grip on the various regs. He’s a great asset here
You’re very kind. I think I will soon have exhausted my knowledge of them.
The effect is quite important because it means that a US private pilot certificate issued pursuant to 61.75 is not bound by the regulations governing the foreign pilot licence and rating(s) contrary to received wisdom.
This seems to have been “discovered” several years ago. I don’t recall the details but IIRC it was something specifically useful for the PA46T (Meridian or Jetprop) which needs a type rating in Euro-land but doesn’t need one in the US and can thus be flown in Europe on a 61.75 piggyback FAA PPL.
Nobody realised this concession has its roots in the 1960s 
Thanks again Qalupalik, I misinterpreted
“FAA has previously held that a US IR test is superior to an IPC so I expect the same holds for a foreign ICAO-compliant IR test (or check)”
a bit, but you brought me back on track.
Also interesting to know, that the validation everybody refers to is a special purpose license.
Peter wrote (#12):
This seems to have been “discovered” several years ago.
If you mean by way of an AGC opinion then it was probably the interpretation to Andrew Krausz of 22 March 2012 from Rebecca B MacPherson, Assistant Chief Counsel for Regulations followed by an interpretation to Henning Grossman of 6 Aug 2014 from Mark Bury, Assistant Chief Counsel for Regulations. The latter interpretation is what you had in mind.
An inspector I met at the Kansas City FSDO in 2001 conveyed the same interpretation.
Nobody realised this concession has its roots in the 1960s
It has a far more interesting history which began at the dawn of WW2 in the late 1930s at a time when Britain and France anticipated needing additional aircraft in the event of war breaking out. See for example Davis, J. Journal of Contemporary History Vol. 20, No. 1 (Jan., 1985), pp. 71-97 [URL: https://www.jstor.org/stable/260491?seq=1#page_scan_tab_contents ]:
The breakdown of collective security and the European crisis
which followed the Munich Conference of September 1938 led the
British government to consider urgently the possibility of the North
American supply of essential war materials. They set up various
missions to consider the possibilities of such a supply, and these
included the top secret Riverdale Mission of July and August 1939
which resulted in recommendations for a New York-Ottawa
organization for a supply of munitions and aircraft in the event of
war.
Only three weeks before Germany declared war on Poland, the US Civil Air Regulations were amended to enable the recognition and certification of foreign pilots for the limited purpose of flying aircraft which might be purchased. At that time the cash-and-carry provision of the Neutrality Act of 1937 had expired and so an arms embargo prevented direct shipment of war materiel to belligerent states. A solution used before the emergence of the Lend-Lease policy was to fly aircraft across the border into Canada from where they would be shipped to Britain, even before Canadian Pacific Railway established the Atlantic Ferry Organization (later RAF Ferry Command). As notified in 4 FR 3648, 17 Aug 1939, the new section 20.69 of the US Civil Air Regulations provided in part that:
…
(c) Any person issued a private pilot certificate under the provisions of this section, before being eligible to pilot civil aircraft of the United States, shall offer proof satisfactory to an inspector of the Authority that he is the duly authorized representative of a foreign person or nation contemplating the purchase of aircraft manufactured in the United States, or that he is the duly authorized representative of the competent aeronautical authorities of the foreign nation in which such aircraft will be registered, and such private pilot shall not pilot any civil aircraft of the United States except aircraft which a foreign person or nation contemplates purchasing, and then only in accordance with such terms and conditions as the Authority may prescribe.
…
TobiBS wrote (#13):
… the validation everybody refers to is a special purpose license.
The term “special purpose” was dropped by the early 1970s when the rule was moved to section 61.75. Special purpose originally referred to limited privileges such as ferry flying new aircraft for export, operating US-registered aircraft in foreign countries, flying for the maintenance of proficiency, and so forth.
