Mount Vernon East is located in downtown Mount Vernon, while Mount Vernon West is directly across the river from Yonkers, so the New Haven station was always the “main” station for the city.

Metro-North continues to differentiate the two in a similar manner: Mount Vernon West shows up on tickets as “Mt V W” or “M V W” while Mount Vernon East is simply “Mt VERN.” Conductors on the New Haven also tend to say just “Mount Vernon,” while on the Harlem I’ve always heard them say “Mount Vernon West,” though the automated announcements have eroded this distinction.

The New Haven didn’t become a part of the Penn Central until 1969, so at the time of printing the two different Mount Vernon stations were on two different railroads. In 1970, they actually tried out the name “Mount Vernon Avenue” but I guess nobody liked that very much, so by ’73 it was “Mount Vernon West.”

Don’t get freaked out, because I didn’t know that off the top of my head. ;) I had to consult my collection of timetables. I don’t collect for the NH, so I couldn’t tell you when that station became Mount Vernon East.