a few examples:

pek = bjs
den = dia

i would not be surprised if, in one or more of the above cases, the same metro code v. airport code confusion that gave rise to this thread is at play, but tmk there is only one commercial airport in each of these cities so it's a non-issue.

edited to add: i just consulted google and found a little more info. apparently, bjs is the actual airport code, but my luggage tags always say pek. who knows?

http://www.jal.co.jp/en/jalcargo/inter/online.html