Preston?
So that's 23. But add other sleeper stops I've missed out and maybe Penrith and it surely runs close?
I'm curious which trains run between Preston and Mill Hill (or v.v.) none stop, as I can't think of any on the top of my head.
Your point about Penrith is definitely correct Southbound, ignoring the current emergency timetable.
The 10:00 Glasgow Central to London Euston via Birmingham runs none stop between Penrith and Preston.
I'm sure there used to be a northbound London to Glasgow which used to run none stop Preston to Penrith, 10:30 ex Euston, but it shows as stopping at Lancaster.