The British got a mixture of AP shot types. That is why sources differ so much when they describe the effectiveness of the shot.
Here is some sources for the 37mm penetration:
"Anti-Tank Weapons" Peter Chamberlain and Terry Gander, MacDonald and Jane's, 1974
37mm M3A1 AP 1000yd 25mm @20º
APC 1000yd 53mm @20º
Tank Battles in Miniature: A wargamer's guide to the Western Desert Campaign 1940–1942", Donald Featherstone, Patrick Stevens Ltd, 1973,
37mm 1000yd 29mm @ 0º
"British & American Artillery of World War 2", Ian V. Hogg, A&AP, 1978.
37mm M3 AP M74 500yd 36mm 0º
37mm M51B1/2 500yd 61mm 0º
37mm AA AP M59A1 500yd 25mm 0º
Not much fun out on the Western Desert if all your tank had was the M74 round.