So this effectively makes the rawk exchange a risk? Even though the club know about it and are apparently happy for this to go on, with the exception of Euro aways which is why there are no Euro away exchanges.
I suspect something underhand on the club/steward's part like others in this thread have said. I have 5 memberships (me, my brother, missus and 2 Croatian friends). My Croatian friends only come over 3 times a season at most so they are almost always spare. I was away in Barcelona for the Bordeaux and Swansea games, Croatia for West Brom, had to work Boxing Day evening in London so missed Leicester, and now I'm in South Africa for Arsenal, Man U and Exeter. I buy all home games automatically in bulk sales as well as autocup as I don't know my schedule months in advance, or even weeks. As the above shows, I can miss a lot of games in spells.
There's quite often different people using my cards. Sometimes on the exchange here, other times friends/family. What I have done for a while is given people the first line of address of each card and date of birth. I stopped doing it but maybe I ought to start again. This isn't foolproof, but it's something to cover yourself.