A few more thoughts -
quite a lot of buffet / kitchen coaches (loco hauled and in multiple units) had different door / window arrangements as the kitchen / serving area was on one side.
the Mk 1 and Mk 3 sleepers have different window arrangements on the corridor side, and the Mk 1s had an additional door half way along the corridor side.
And the engine compartment of Southern Region diesel units (Hastings, Hampshire etc) had the engine offset towards one side, so there were radiator grilles on one side and windows on the opposite side.