I think the Chipmunks were used for initial CPL GFTs.
GFT 1 - Navigation
GFT 2 - General Handling
GFT 3 - Instrument Flying
GFT 4 - Night Flying
The Doves were used for initial Instrument Rating tests.
Initially all 4 GFTs were done in the Chippy but then something happened to make them rethink and after that only twins (Doves?) were flown at night.