I think you need to review each event that the override is used to see if clinically appropriate or not and why this was used if it isn't an urgent situation. If frequent - then it could be SABRE reportable as there is potential risk to the patient from untrained staff collecting units and potential risk to the blood units too.
Why don't you give Chris Robbie a call at MHRA to discuss this- he is very helpful and i'm always calling him about things I am unsure about.

bw