I am pretty sure the buffet car in the 225 sets (Mk4s) were turned during 'Mallard' refurbishments and so, I think, should only be 'reversed' in 225 sets with red doors. Thats what the brief in ticket offices was, at the time.
Intercity/GNER Standard 225 formation:
91-TSOe-5xTSO-Buffet 1st-2xTFO-DVT
Intercity/GNER Pullman 225 formation:
91-TSOe-4xTSO-Buffet 1st-3xTFO-DVT
GNER/NXEC Mallard 225 formation:
91-TSOe-5xTSO-Buffet Standard-3xTFO-DVT
The small windows on the Mk4s go at the same end, except on the buffet standard.
Intercity/GNER Standard 225 formation:
91-TSOe-5xTSO-Buffet 1st-2xTFO-DVT
Intercity/GNER Pullman 225 formation:
91-TSOe-4xTSO-Buffet 1st-3xTFO-DVT
GNER/NXEC Mallard 225 formation:
91-TSOe-5xTSO-Buffet Standard-3xTFO-DVT
The small windows on the Mk4s go at the same end, except on the buffet standard.