Sluggo said:

So if these three destroyers that are being overshadowed by the Executor,

why can we only see two of them?

You'd need to ask Lucasfilm.... ;) I think I may have a reasonable 'possibility', as to what happened here, but I'll first need to organise the intervening screenshot that occurs between these two, to better explain it. By the way, if I remember correctly, the 2 Stardestroyers in the distance of the top shot here were already 'lit' in a 'half-shadowed' manner, and that it is only the nearest (biggest) one in the shot that is being 'overshadowed' by the 'Executor'. But I'd need to check.

Darth Solo - Han??? 'mock-ups'??? Late night I take it! ;)