The general assumption in dealing with computer systems should always be to assume that they contain bugs. There have been detailed studies in the defence and medical industries into flaws in critical computer systems, and bugs are endemic in complex computer systems. We should always be prepared to question the results we get, check, test and double check.
In critical cases where there is a question about the validity of the results, they must be checked. In these cases they were not checked, they were assumed to be correct because the subpost-masters and mistresses in the case could not provide evidence that the software was wrong. But then, how on earth could they?
Questioning the validity of results and working hard to validate test and audit results is an approach that is well supported by the evidence and has served me well in my professional career.