There are reports of telephone contacts between Europe (for example, a bar next to a mosque in Madrid) and the hijackers in the U.S. days before 9/11. If you faxed this kind of letter on the European-size paper to the States, could a fax machine here require or prefer the European-size paper?
All the letters are said to be photocopies. (It's obvious that at least one of each pair is a photocopy, but I've that, in fact, they didn't mail any original.)
They don't have the low-resolution appearance typically seen in faxes.