1) Isn't the council photo supposed to show the signage of the restriction together with my VRN so that I know exactly what I failed to comply with, rather than just the enigmatic 52(M) code? And
There is no legal requirement for any photographs
at all on the PCN. Any photographs you might see on their website are stills from the video. It is commonplace, though, to see photos on the PCN of the car at the relevant location, but often the camera is not positioned to show the sign and the car going past it.
2) Is not the PCN supposed to tell the owner that if they make an informal appeal and fail, they still have ANOTHER 14 days to pay the discounted penalty from the date of the rejection?
The reoffer of the discount when rejecting informal challenges is not a legal right, funnily enough, but most councils to commit to re-offering it, but there is no legal requirement to put anything about this on a Regulation 9 PCN (one served to car or driver at the roadside), nor on a Regulation 10 PCN, (one served to the keeper on the V5 )
However, your's is a postal PCN, so there is only one opportunity to submit representations. These are formal reps, there is no informal challenge stage. The discount period remains extant until its end date, but some councils play hard-ball and refuse to re-offer the discount if their rejection is past the discount end-date. Most councils do, howver, re-offer the discount. If they didn't, they'd make a rod for their own back, because with no discount re-offer, it is then a total no-brainer to take the council to adjudication, the penalty does not increase, nor are there any additional costs. The council, though, have to prepare an evidence pack.