As someone that works in IT at a fairly senior level, I can tell you now - with 100% certainty - without a shadow of a doubt - that any and all bugs would have been held in a defect log / risk log populated as a result of significant user testing and the decision to 'go live' would have been with the Post Office.
To do so, they would have had to a) sign off on the known issues b) accept the risk and mitigation of those bugs
This is standard procedure for all new IT systems.
If the customer does not accept those risks, then a commercial decision must be made to either spend more on development or buy out the contract and scrap it. Or more unusually to agree to go live but have financial service credits to cover any losses due to those known issues experienced by the business.
As they went live, the PO must have known the issues and proceeded anyway. We don't know at this time what the commercials are behind the decision or even if there was one. My personal opinion (and backed up with having worked on IT projects for govt agencies) is they are all a) inept b) terrified of reporting issues to the higher political masters and will therefore cover up any issues and blunder on regardless. Add to that the penchant for them to regularly move the goalposts every 5 seconds - don't forget the DWP pulled out of this joint venture at the last minute, it doesn't surprise me it had issues.
The fact that it has become abundantly clear that the PO prosecutions mandated the sub postmasters not declaring horizon faults for a lower charge, or that the investigators refused point blank to look at transactions and transactional code in the system leads me to believe they knew what bugs there were and HAD signed them off, but wanted to cover up their decision to go live and use the system with bugs, by falsely prosecuting the little people.
Typical government agency cover up con-job
As for the remote access piece...well of course the IT supplier has remote access. But if you think any engineer would remote on and just **** about changing stuff for sh1t5 and giggles, you are as deluded as the typical daily wail reader. The decision to make changes will be issued by the post office nbsc desk as part of a service request or operational change and then handed to the IT provider to perform. It would not surprise me one bit if it comes out there was a constant stream of these requests from the PO to correct obvious large scale errors and issues for major accounting errors that would be hard to hide from superiors or the press....but the smaller ones were left with the sub postmasters holding the can
I cannot see how Fujitsu are culpable for this unless it comes out that they purposefully hid the defects for 15 years and paid off every barrister, solicitor and investigator in the PO employ to hide this fact and prosecute the sub postmasters erroneously.
Otherwise if there was an identified issue leading to a 20k accounting shortfall, the PO would just approach the supplier and fine them a service credit, write off the amount and at the end of each financial period, settle up the accounts and if there was a real shortfall, the supplier would be liable
Just think about it for 2 minutes before jumping on the band wagon and braying for Japanese blood.
This is no different to any other government screw up and cover up since ... Well forever