Pretty sure I saw them use an S15 in Southern livery too. Which would be wrong in at least three different ways.
My favourite of this trope was in the recent revival of the Darling Buds of May when one of the characters says something like “it’s a class 5!” and it was the sodding Q class! As if...
From Russia with love, the external train scenes (showing apparently a journey from Istanbul to Vienna) featured an LMS Black Five and some southern green coaching stock. I know it's petty but this kind of thing winds me up.