Re: Black and white or various shades of grey?
Rather fatuous argument to be honest.
The question in this case appears to be whether the access was authorised or not. To stick with your speeding analogy, let's say the speed limit on a road was changed from 40 to 30, but the signs weren't updated and still read 40? Would you be breaking the law going at 40?
Here it seems that, until the letter sent a year after the case, the entire system was operating under an assumed access authority, with what was authorised and what wasn't authorised being unwritten and unclear. In this case, she had a reason to access the information (to confirm or otherwise a conflict of interest), and in the absence of written rules, or established ACLs, it is impossible to say whether that reason was legitimate or not. As such, you can't say whether the Computer Misuse Act was breached or not.
Given that a jury trial is extremely expensive, judges are expected to throw out cases where the CPS haven't done their due diligence and prosecuted with a reasonable expectation of a conviction.