Prior to the Internet stampers didn't know much about what was being created beyond their community. Once the Internet got established generally stamping sites or challenges didn't specify size requirements. But I recall often reading the reason for A2 cards was explained: it is the most efficient use of a sheet of paper; envelopes were available and it could be mailed at the lowest letter cost. Once I started swapping internationally I received cards that were 5.5x 8.5. I don't recall seeing background stamps that large but I did receive a few 9" stamps as RAKs. Some have always made 6x6 and 5x7 cards. Last year when I was making mixed media cards I often found I needed the space of a 5x7.
