The FAA received more than one Grumman G-21/JRF
Quite correct and also note the statement the numbers are for "combat planes to England" not to any other destination, so none of the 20,368 aircraft reported in AIR 19/524 as Deliveries of aircraft from North America to Commonwealth countries and forces outside of UK, excluding pre war UK contracts, to September 1945. That said it actually only records 2 Goose to Canada in June 1940.
numbered FP475 through FP524
Apart from new production aircraft ex civil versions were purchased.
USN details,
order LL-86447 dated 16 July 1941. The order was 50 JRF-6B, serials FP475 to FP524. With FP500 to Bolivia and FP505 to FP509 to US Army. 2 P&W R-985-AN-6B engines, acceptances in first 6 months of 1942 were 3, 5, 6, 4, 4, 3, then 4 in November and 2 in December 1942. Then 5 in January, 4 in February
and 4 in March 1943. Notes are 6 converted to JRF-5, 1 for Bolivia, 5 for Army, 25 for British Air Commission, "Goose IA" . The JRF-5 (US Army designation AO-9) for Bolivia was accepted in July 1942, those for the US Army, 2 in November and 3 in December 1942.
Order NOs(a)-463 dated 2 October 1943 for 30+31=61 JRF-5, of these 4 to UK, FP470-3, plus 12 to Canada and 1 to Iceland apparently listed under RAF serials FP457-69 (RCAF serials were 382 to 393) The RCAF also reports operating FP471 and 473. Acceptances for Britain 1 in January, 1 in March and 2 in April 1944. Canada 2 per month February to May 1944, 1 in July, 2 in August, 1 in September 1944, the 1 for Iceland in July 1944.
RAF Contract cards, order BSC666 for 50 Goose IA, Grumman 21A, only one contract card present, FP475 to FP500, blank entries for FP495 to FP497 and FP500. Deliveries were 9 in March, 6 in May, 3 in June and 4 in December 1942, so 22 definite arrivals.
No entries in RAF Serial Registers for FP470 to 524 but they do note FP740 and 742 as Goose, returned to US "recaptured" 11 April 1946, US Naval Air Station Miami.
Air Arsenal North America states Goose c/n 1049 was Lord Beaverbrook's G-AFKJ becoming MV993, while HK822 was c/n 1055 ex NC3022 sent to Middle East via British Ambulance Air Corps purchase. No mention of FP738 to 947. MV993 was probably the one that arrived in Britain in July 1942, hence being designated a G.21.
Pearcy adds FP474 and FP738 to 747, to the list in Air Arsenal North America of which FP738, 739, 741, 743, 747 retained by USN, given the Serial Register entries it is quite possible all of FP738 to 747 stayed in the US.