To be honest, IMO you would not succeed in convincing an adjudicator on (b) or (c), primarily because you could have parked on the carriageway instead. This is based on reading decisions which, because the adjudicator cannot consider mitigation, at times seem cold and harsh.
But if you thought you were parked in a parking place, then different rules apply.
IMO, I would go for contravention did not occur because you believed you were parked in a parking place covered by the upright traffic signs* restricting use to types of permit holders but also exempting assisted alighting which applied in your case as you were ***********.
Are you local and could you get better photos of the markings please. On GSV it looks like a continuous bay with the 2 signs sitting inside.
What property were you parked outside? The numbers are distinct on GSV which would allow us to pin-point exactly where you were.
Objective:
to shift the focus from exemptions applicable to footway parking to those applicable to parking places;
Also, but perhaps later, to tie them up in knots. Their parking places are not lawful or the yellow line isn't, or maybe both! You cannot have a SYL restricting waiting forming one boundary of a parking place which permits parking when those restrictions cover the same times. And (from reading stamfordman's link) the signs aren't prescribed for use anyway unless the parking place already sits within an area where the footway parking prohibition has been lifted.
*- in the plural. Looks to the casual observer like a long parking place within which sit 2 traffic signs.
