actus reus:
As for the T10, it originally had a narrow chord rudder which meant that there was a strong possibility that the rudder would be 'blanked' during a fully developed spin.
My research (and I bow to Chipmunk owners/ experienced fliers of same both of which I am not), seems to show that the production version had a broad chord rudder fitted and anti spin strakes.
A quick Chipmunk history lesson, if I may.
All UK-built Chipmunks, be they T.10's, T.20's or Mk.21's, left the factory without strakes and with narrow chord rudders. A broader-chord replacement rudder (easily detectable by the distinct kink at the bottom of the trailing edge) was developed/approved in 1951 but it appears to have been retrofitted over the ensuing few years to the existing fleet commencing in 1953 (i.e. post production). It should be stressed that the larger rudder was intended to improve rudder authority during aerobatics and cross-wind take offs & landings, as well as reducing rudder load during protracted climbs. Despite that hoary old myth, it had NOTHING WHATSOEVER to do with improving spin recovery. The unintended consequence is that it may have made spin entry easier. Keep in mind that by 1953 a large number of RAF Chipmunks were already ear-marked for disposal (with the disbandment of RAF Reserve Command) and these aircraft never received the broad-chord rudder, which explains why all of the 60 odd ex RAF Chipmunks that initially came to Australia (deliveries commencing in 1956) still had the narrower rudder.
The strakes were fitted quite quickly to the existing RAF fleet in 1958, and certainly were intended to improve spin recovery.
With three exceptions (two Portuguese OGMA and one Canadian-built) all current Australian Chipmunks are UK-builds, and all four possible combinations of "tail; feathers" are present:
Narrow rudder/no strakes
Narrow rudder/strakes
Broad rudder/no strakes
Broad rudders/strakes.
I hope this clarifies the story.
Cheers.