Rest easy. Your stamp is perf 11x11, thus *not* a 423D which is perf 10x12.
Remember that gauging perforations involves a rate, not a count.
Add:
Here are two images of your stamp, note the perfs align, thus they are at the same rate.

Add#2:
And for comparison, here is Scott 541, which is perf 11x10. The top hole is aligned and the different
rate shows up as the holes align, then don't as one looks down the row where the ywo images abut.
