The objective facts:
Your car was parked o/s 54/56 (the PCN states 54 but the CEO's photo suggests 54/56).
The suspended area in that part ran from 48 to 58.
There is a normal traffic sign o/s 50 and also one o/s 62.
You were parked approx. equidistant between the two facing towards the higher numbered properties.
The CEO photographed the suspension sign attached to the traffic sign @ no. 50.
Now, you say 'I had to walk 100 metres to my parents house, find a ticket, fill in the ticket, walk back to the car and display the ticket. For reasons I can't explain, it didn't register to check the signs,'.
Perhaps we can. There is an obvious answer, which is that you walked towards no.62 and there wasn't a suspension sign there, which is why there was nothing to see.
We have this issue on a regular basis i.e. councils not placing suspension signs beyond the suspended area in some odd belief that a suspension sign, even if some distance from where a car is parked, has magical and magnetic properties which draw drivers even if this is not the direction they would exit the suspended area. In this case, as the furthest extent of the suspended area was no. 58 then as this is obviously closer to 62 than is 50 and clearly visible the council was obliged to place a suspension sign there.
You could check with the council before submitting a challenge.