This is like a recent Barnet PCN.
See the sign at Item 14 in the Part 2 sign table:
https://www.legislation.gov.uk/uksi/2016/362/schedule/7/made(these can be seen in the parking places)
What do they mean?
As regards the regs they mean:
Vehicles may be parked partially on the verge or footway during the period indicatedBUT these are area signs i.e. they act as gateway signs and indicate either beginning and direction of the area in which the relief applies or, without arrows, may be used as repeater signs within such an area.
They ARE NOT to be used in parking places which have their own signs:
Item 3, Part 4 Sign Table:
https://www.legislation.gov.uk/uksi/2016/362/schedule/4/madeSo, what the hell should a driver infer from the sign immediately behind where you were?
There aren't any 'Marked Bays' which delineate areas where the London-wide footway parking prohibition has been disapplied. Instead, there are parking places designated under RTRA and partly placed on the footway. Chalk and cheese.
The idiots at the council don't know the correct traffic signs, but what's new.
So, the parking places are marked improperly. But how could that help you because you were not parked within a parking place?
You were parked on the footway where prima facie you were neither permitted by virtue of a resolution nor because you were within a parking place partly placed on the footway. For good measure you were also on DYL.
Nothing you have put forward so far is anything but mitigation IMO.
But you might as well appeal because the discount isn't on offer.
I suggest 'I rely on my representations' and then wait for their evidence pack which you would scrutinise to see how the council has approved parking on the footway in the parking places.