Re: Roll out new point of sale system, get petty crime wave?
To be fair, implementing a more robust accounting system could EASILY generate that kind of response, things that were totally missed before because there was no way to check them, but which flag up immediately in a newer system.
And judges are not there to do the research for you, they judge the case in front of them based solely on the evidence in front of them. Anything else is dangerous. It would be for the lawyers (especially defence) to say "There have been X hundred court cases in recent years because of the Horizon system, which is far in excess of the previous system, can you account for that? Is it not possible that my client is one of many being unjustly accused?"
Fact is, many of the people that went to court PLEADED GUILTY because they were advised to do so. In that instance, neither the lawyers or judges have much to do beyond dotting the i's and crossing the t's. It's why you never plead guilty to something that you know you didn't do. You've basically said "Yes, I did that, exactly as described." and there's no way back short of a pardon or major scandal.
But a new accounting system suddenly detecting 100's of cases of potential fraud over 16 years (so barely 50 cases a year), out of about 7000 subpostmasters, their other employees, etc.? Yeah, it's significant but it's not implausible. Especially when some of those pleaded guilty and in the process even accepted the evidence from Horizon was accurate.
If you were to suddenly implement "insider trading laws" on 7000 stockbrokers and their employees and departments, I would bet that you'd find more than 100 cases a year.
The real problem is the Post Office's rather unique ability to act on its own: "when an organisation is allowed to act as a prosecutor when it is also the victim and the investigator of an alleged offence".
i.e. crusty old laws with no modern need for them and people able to run amok and avoid oversight.
If they'd had to push their case through the normal entities (such as they had to do in Scotland and Northern Ireland), the number of instances would have been less but still might have flagged something in people's brains along the way.