This would be the biggest tell as I don't even know where you would buy Letter paper in Europe. It's hard enough to buy A4 in the USA. I'm in the USA and I'm a jerk who prints things on A4 and mails them out just to make sure they don't fit in anyone's filing system.
A4 is a bit smaller than US legal, based on a glance at wikipedia.
Surprised it's difficult to get over there. I thought it'd be desirable for design work.