I had several requests that were still listed in my "books you requested" section long after the "will mail by" date expired... a couple are now "en route" but others are in the cancelled TA and are not showing any reason so did they finally time out or did the sender manually cancel them???  Just wondering...

How long do you mean by "long after"?  People have 2 days to mark mailed past the will mail date.  If it;s really any longer than that, there may be a bug.

For your other Q - If it has timed out, when you hover over the X, it'll say "no response from sender after allotted time".  If they canceled it, it'll say "canceled by sender".