I think most of the drawings aren't considering the ledges very seriously. At the moment I'm not even sure what they are, either roof or floor for the bridge wings or part of the mast.
the way i see it, the ledges could be
A) mockup related but not ship related. But not only can i not think of a purpose why they'd need such a ledge just for construction purposes but also those ledges happen to follow the line of the top of the last deck. A simple temporary ledge/balcony for construction purpose would be quite crude and not precisely follow the other lines of the ship. which i don't believe option A is even plausible.
B) ledges are going to be part of the final ship.
B.1) they're part of the third deck as a vantage point for the command bridge, for docking ops and various needs, more like a balcony. - but those balconies seldomly are enclosed and if they are - who builds the roof first, then the rest of it? furthermore, there's no provisions visible on the third deck for such an extension, that side of the command bridge deck looks like a finished product.
B.2) they're part of the fourth deck, either as the vantage balcony or actual enclosed structure on top of the third deck, possibly even housing radar systems. - possible, but it'd mean command bridge is going to be on the fourth deck. only reason why one would nowadays have a high positioned bridge is if radar arrays are below it. More plausible variant would be the command bridge on third deck, as it'd already have a vantage point looking backwards, as there's that large walkway behind the forward superstructure.
B.3.) perhaps most plausible solution that i can think of is that the ledge is going to be a simple platform/railless balcony that will house some sensors that aren't going to be enclosed in the larger structure. like various el. emission receivers, comm antennas etc. And that for some reason they couldn't have been placed on top of the superstructure roof itself, as they need extra spacing or the roof is going to be taken by a large array-housing structure (as elements on that also need some spacing to clear the other elements) and so on.
But what additions do you speak of that could be more easily constructed from the start? It seems to derive itself from what we solidly can see from the mock up superstructure right now without too much artistic license.
while anything is possible since the mock up clearly isn't finished, i don't see much logic in first floor over the main deck missing anything but side walls to connect with the edge of the ship. i'm talking about mock-up building process here. And we might even not see that finished ever, if there's no need for it. To have the large, uninterrupted surface in the same level as floor of second deck i believe we'd see the the back part of the front superstructure (the one that's one deck high) already as wide as the ship. But it doesn't look as wide to me. Plus some holes on the side wall of the first deck that supports the main structure walkway with large windows. But that wall also looks quite finished, as if there is nothing to be added there aside of the sheet of metal to act as an outer side wall.
All that being said, i actually like the idea of enclosing the vls bay with walls, as the drawing suggests. Of course, if one did it with aft vls bay, it'd be a crime not to do it with forward bls bay as well.