OP, I think they've given you an out!
On ** I parked my car and interpreted the sign as meaning that parking by non-permit holders between 6pm and 8pm was unrestricted.
Although it is clear that the CEO also considered that non-permit holders may park without charge at this time, they still issued a PCN.
As the authority will see, and I can see on reflection, the restrictions are as follows:
Permit Holders only: ****** and 6.30pm to 8pm on Saturdays;
Shared use: ******.
The PCN was issued for a contravention 12S at 7.44pm. But this is impossible as explained below.
As I now know, at this time the restriction is permit holders only for which (preferably) code 16 is used or code 12(R) indicating a parking place whose restrictions at that time reserve parking to permit holders(in this case E). 12(S) means that parking is shared use, in this case permit holders or pay by phone.
If this sort of misunderstanding is accepted from a CEO who is familiar with their patch and has been trained to give a high-class service, then it would be grossly unfair, and therefore challengeable, to impose higher standards on motorists who, as in my case, were parking for the first time.
And if I may pre-empt any response which might refer to the use of suffixes as not being mandatory, I think the authority will be aware that these are considered essential when the convoluted code 12 grounds are used. However, whatever options were open to the CEO at that time and the authority now, using the wrong suffix is not amongst them because doing so has the capacity to, and in my case did, mislead.
-***( you can insert these!.