Thanks to all who responded! We'll hope for the best and the worst case scenario is we get pinged for $160. The responses have made us a little more hopeful that won't be the case. We'll have the documentation ready to argue the case if necessary (thanks to all for the various links - that agencyconnect reference seems to be particularly useful!), but it's not worth too much stress at the start of that 20+ hour trip home. I'll just warn the honorary treasurer that there may be a slight budget revision on the day. Thanks again.