Cut Corners On Classic Stamps?

I've got what I'm pretty sure is a Scott #408. No big deal - low value "classic".

But it has cut corners (see below). I've seen this occasionally on other older "classic" stamps.

Was this a way people mounted them in albums in times forgotten? Or is there another explanation?

BTW, this is the very famous Scott Type A140. If you have a stamp that is like the one below, there are literally dozens of possibilities of what it actually is.

Not caused by a collector, but deliberately made by the US Automatic Vending Company as a privately produced coil.

The stamp will be listed in the Scott US Specialized in the section on Vending & Affixing Machine Perforations.

Wow! The US Classics are sooooo complicated.

khj, thanks for that. In fact, I'll be posting another stamp tomorrow which I just found in the Vending and Affixing machine area.

Thanks for the stamp collecting lesson. I gotta get something ready to give away in a contest to pay back for my SCF tuition costs!