YOu seem to be assuming your out-of-time declaration will get you back to the Notice to Owner stage. Please tell us why you are having to submit an out-of-time declaration. All the declaration does is get you back to the Notice to Owner stage, you don't put any of your arguments against the PCN on it, you have to explain wny you are submitting an OOT declaration. If this is not accepted, (and they are usually refused), you are back to the bailiffs.
As regards your proposed appeal argument, the short answer is no, they won't. Photograpshs for parking contraventions are not even a legal requirement, and there is no mandatory observation time. If you were loading then it is up to you to claim the exemption when responding to the PCN.
The original PCN was for parking where there were parking and also loading restrictions, so even if you were loading, if it was in the restricted time, you cannot claim the loading exemption.