We are relying on Community sources like https://adapools.org/groups/ to see if a pool is a multi-pool or not and I understand everyone has a different definition of this.
See the methodology of the pool group definition on Adapools by Daniel Ribar here: Cardano Donuts - Methodology - Daniel Ribar - Google Docs. (providing a service for pools that are then completely independently marketed is not part of this definition)
Unfortunately, it is a fact that some people with good brands do not run their pools themselves. One can like it or not, at least Holger has never made a secret of it. There is probably a high number of unreported cases, but this should be considered separately from the other community contributions.
PS: I have separated several posts here from the other thread to create this topic here.