I suspect that most tandems that get a lot of mileage have tires 30mm wide or less. Most 28mm or less. The few high mileage tandems using 38mm tires also have some captains that build there own wheels. This would leave a small percentage on shop built tandems.
All I know for certain is that I had two wheel builders build up wheels and 6 rims out 6 rims fail. These rims where intentionaly purchased 2 at a time at different times. Some were before the move to the US and some after. That seems like a pretty good test of the design. The change of 3 pairs out of 3 having the same rare manufacturing defect seems small to me. The math clearly indicates that wider tires stress the design more and would reveal weakness of the brake track due to the length of unsupported height below the tire bead.
Likewise 4 out 4 of Velocity's A23 rim with a short rim wall have not failed in the same usage on same bike at same inflation on same roads with the same riders.