Is it much work to build? Usually these things are pretty clear.

Although if we ever get more people contributing directly via GitHub and I'm no longer using my mental framework that catches most of these things, it would be more valuable.

The threshold could probably be set much tighter than 10%. I don't know that I've ever seen one off by more than 5%. I was going to say 1%, because even that kind of deviation is pretty uncommon, but on the rare <250-mile routes where we get the true Aeroplan distance thanks to a non-status person, even a mile or two would trip that.

Would it be better to make it a fixed number of miles? Even really long routes are rarely off by more than about 20 from haversine. Then again, 20 miles on the 37-mile YYJ-YVR route would be a huge mistake.

Or both? Flag it if it's off by either >2% or >20 miles?