When did OX come out? I was also wondering the same thing about the power switches on the west leg of the "Y" at Ayer. Was it part of the 4R project?
How about Slab City, was that a 4R creation too?

don;t know when it came out but it is still a station in the timetable...there is also an interlocking called "Gallagher" next to the new station which was opened a few years back