My preferred approach is to set the scene first and clearly.
I hold a resident's permit for zone ** and on ** (no idea, you've not said) I parked my car as can be seen in the authority's photos. At this time I did not see any signs advising of a forthcoming suspension. My car remained parked until *** (I was on holiday from ** to **) when I returned to my car and found 2 PCNs issued on ** and ** respectively both citing the same contravention, namely *****.
I inspected the suspension signs which stated that my bay was suspended from ** to *** for '***** (works) to be carried out by ***'. I discovered subsequently from *** that ****(no works), neither were the bays used for any other associated purpose as can be seen in the CEO's photos of my car.
Is this the story when the gaps are filled?
IMO, then you make your arguments e.g. for both PCNs the penalty exceeded ...circumstances of the case, these being that as no works took place the suspension as such was void and as the signs were not erected when I parked the council failed to give adequate notice of the suspension; for PCN 2, this is void by virtue of any contravention being continuous etc..
Then...
If the authority reject my representations on the grounds that the signs were in situ before I parked and gave adequate notice then they are required to provide proof in support, a simple claim to this effect being both insufficient and suspicious. If the authority...the bay was used for the stated purpose then again they are required to produce evidence in support e.g. CEO notes/photos etc. Finally, as regards PCN **, why, when the car had remained stationary, the demand for a second penalty predicated on a single act of parking is lawful.
Just some thoughts.