I hear the trials for the baggage system were only tested with a few hundred empty bags, nothing like peak throughput of a busy week day morning check in.
I have heard exactly the opposite. The system was tested with more bags than it has yet had to cope with. The "rumour" is that the people who program the software, the BAA, never changed the codes for a "real" day, and the system failed to recognise any bags at all. Despite repeated asking from BA to the BAA, they denied a software problem. Eventually after 3 days the BAA admitted the mistake.
Just one of many many stories circulating.