( and the Chipmunk) were both designed to RAF requirements, not civil standards.
Structurally, they were accepted "as is" for original civil certification (let's not argue about anti-spin strakes)
Leady,
Fair point regarding the DH.82, but the Chipmunk Mk.21 was built "ground-up" as a civil aircraft, and certified in the UK, from December 1950 to September 1951, as an aerobatic category aircraft.
Also, at the risk of nit-picking, in reality they're spin-recovery strakes. If they actually achieve anything is another issue!