Currently using both holes. Attached is a pic of one of the windows that is still intact. On the other windows either the pivot bar has completely rusted out, the shoe is broken, or both.
I tried removing the second screw and leaving the bar with just one screw at the 2" position and it seems sturdy enough -- but that's not the way it was designed. If you can't find the bar with two holes, I'm sure it would work.
These vinyl windows were installed at the end of 1997 if that helps you source the parts. No logos or nameplates or stickers that I can see, so I don't know what brand they are.
Thanks.