Have you ever seen valve pipe get cut like this?

[Pman6]

I changed a Mixet valve today, and was surprised to see a cut in the pipe thread.

Maybe the previous homeowner cut it, or maybe the plumber back in 1966 made a mistake?
or did mixet valves come like this?

 

[hj]

That slot was for a "moon" shaped clip that prevented the stem from rotating 360 degrees. IF you tried to remove the stem without removing the clip you would break the front of the valve off.