The non-USA/non-Japan ones were sent during the Con itself in light envelopes. Some survived the rigors of international sea-mail better than others.
This may be true. However, I did
refer to USPS media mail. (I live reside in California.)
No, I did not notice the postmark on what was left
of the envelope, so I don't know from where it was sent. But taking what you said as accurate, because I did not attend the con (not for lack of desire), and
I reside in the US, this would mean that my book was not
sent from Japan.
My original point still stands: "Why whoever sent it thought a flimsy envelope would be strong enough to withstand the "tender mercies" of USPS media mail
escapes me. It's a wonder my book wasn't ruined." (Emphasis added.)