It's similar on XC.Traveled first offpeak day return Derby-Sheffield last week (with a railcard it’s only about a fiver more than standard, but full catering including breakfast roll one way and wrap the other was offered by EMR). Train manager, checking tickets, said: “Can I see your other tickets please.” “What other tickets?” I replied. “Oh, I presumed you were splitting. Not many people buy first just for that journey.” So some staff are very familiar with splitting, and almost assume its being done on some flows.
I'm usually on XC (in standard) heading south from Sheffield, the guards typically ask any Derby ticket holders if they have any other tickets. Most do!