One example of that is Markit Group, which had revenue of *$1.5bn/yr* when it me...

One example of that is Markit Group, which had revenue of $1.5bn/yr when it merged with IHS in 2016 at an implied valuation of roughly $5.5bn. Best London startup of the last 25 years, including DeepMind, not close.

https://en.wikipedia.org/wiki/Markit

Being a trusted third party is frequently an amazing business, if you can earn or negotiate your way there.