The Bulldog had a strict limit on fuel asymmetry for spinning. Students were always required to keep the left and right tank contents in balance, so often the selector was moved from the 'BOTH' position to achieve this....
The only delayed spin recovery I ever encountered was when my (very good) student entered a right hand spin. It didn't seem to want to recover, so I thought that he must have relaxed the back pressure too soon before applying full left rudder. So I took control, re-applied full pro-spin, then recovered, but again it took a while....
I wrote up the trip in Bloggs' notes, but later we found that one fuel gauge was sticking and was hugely in error. So in large red pen I amended Bloggs' write to say "Not his fault - aircraft had an unserviceable fuel indication system!".
Keeping the ball in the middle and the fuel selector on 'BOTH' would probably have kept most Bulldogs' fuel in better balance than believing the useless fuel gauged and balancing as indicated.
Quite why we lived with such a well-known snag as the Bulldog fuel indication sysem for so long beats me....