So on a typical 747 flight 40 people will have their luggage lost when we get to the reclaim? That seems really improbably high. How come I don't see hundreds of people standing around getting angry at the belt?

At Heathrow, it'd mean 20,000+ people a day with lost luggage (if they all checked luggage). You'd need more than the entire taxi fleet of London to get their luggage to their hotels.

Really doesn't pass a common-sense check.

Bags are lost often enough there’s a charity selling the bags that never get claimed.

https://www.unclaimedbaggage.com/pages/how-it-works

They say a 3 month search, but if you read around you’ll see 5+ days and your bag is basically gone. They say .03% of all checked bags end up lost and then unclaimed. How many must get lost to reach that unclaimed number?

It could be as high as 10% if you have a connecting flight, maybe? I’ve been fortunate enough to always fly direct and never had any lost baggage. I’ve always assumed direct is fine, it’s once you start transferring loads across different flights and codeshare carriers it starts to do awry.

Of course - but it's an indication of the ludicrous scale.