Per John Becker, it is very likely a stamp from a booklet pane. The one listed by Scott as 634d (perf 11x10-1/2):
The extremely square corner is the tip-off as are the very straight cuts. This is hard to do with scissors or even a chopper-type cutter. It could be done with a mount cutter, but there is no reason to do that.
You may wonder why the cut is not perfect. It might be just age. The original paper is rather soft and would get slightly ragged edges when cut, particularly if the blade had tiny imperfections from constant use.
A pile of printed sheets is cut with a guillotine-style blade with the sheets securely clamped down to prevent them from moving around. Clearly, the intent is to not cut off parts of the design, but stuff happens, and these were deemed good enough for release. The situation for booklets of this era is that sheets of stamps with interleaving sheets between and sandwiched between sheets of the eventual cardboard covers are stacked and cut. Since the stamp design can't be seen at this point and may not be perfectly aligned with booklet cover printing or its cutting marks, you get a result like this. More than you maybe wanted to know, but there it is. And this miscutting is/was fairly common.
So, this stamp is not damaged, but it is in a pretty low grade to collectors who (in the US, at least) prefer well-centered stamps.