MelforDMThemes
says
Since including the PSD is optional there are no guidelines. It is often not even possible to have the exact same PSD as the HTML version because of the reviewing process which may take some improvements you don’t want to add to the PSD afterwards.
It’s a bonus, it doesn’t matter if you only include some backgrounds and buttons or the whole layout.
All the best 
Stupid me, posted with wrong nickname, sorry!
