Just for info. I'm currently on board the 17.36 Harrogate to London King's Cross service. 62 passengers on board departing Harrogate (6 in First Class). About 20-25 were already at Harrogate ahead of the previous Northern departure to Leeds (17.16) and didn't board the Northern service, thus implying they are travelling LNER beyond Leeds). Quite a few passengers with luggage, also suggesting they're travelling beyond Leeds. Unfortunately the electronic seat reservations haven't been switched on. Of course, 62 passengers will fit comfortably into one carriage of a 150, 158 or 170...
The train is also advertised (on the Azuma CIS) to stop at Horsforth, despite It being a "pick up only" stop in the timetable, so in theory, no-one should get off there...3 passengers did!
Another 12 passengers waiting at Horsforth, but I don't think they have all boarded. So probably a total of around 70 passengers on board as the train approaches Leeds.
Would there be more passengers if it were a Bradford - Shipley - Leeds - London service...?
The worst thing about the Harrogate - London direct services is that too many of them are only 5 car trains and are not strengthened between Leeds and London (despite there being sufficient time in the schedule to couple another unit at Leeds). A 5 car train between Leeds and London is usually pretty cosy, no matter what time of day it is, and this train is still a commuter service for passengers travelling back from Leeds (departing 18.15) to Wakefield, Doncaster and possibly even Grantham.
Not sure if my post answers the OP's original question, but adds a bit of context.