Sometime between 1967 and now, did the service go up to three trains an hour before moving to the two trains an hour now?
Don't you view it as being four trains an hour at present - two none-stop and two calling at intermediate stations?
Depends on the hour, doesn't it? It's four per even hour and three per odd one, during the day. That's what the timetable says, anyway, but obviously subject to short, medium-term, and even longer-term changes now.