That doesn’t mean anything as TPE have been using 6 cars on this route for years, Can it take 6 cars with all doors on the platform?
Despite the mention somewhere upthread of the platforms being lengthened as part of the TPRU, the answer seems to be no.
Whilst I wasn't on an the train in question, I was in Manchester Victoria this afternoon and heard the automated announcement about a TPE service due to leave. 11:59 to Redcar, doubled Class 185.
It listed various stations where you had to be in the front X amount of carriages. Brighouse was definitely mentioned, but I can't remember what number of carriages it said. If I were to guess, I'd say most likely five. Both Hebden and Sowerby Bridges were also on the announcement as having carriage conditions.
Pretty sure Grand Centrals 5-car Adelantes fit into Brighouse without selective door opening.