Obviously the DM summits were not invalid when they were valid!
The reason why they were valid when they did not meet the prominence requirements was because of an old exception in the General Rules that allowed non-prominent summits to be included on the discretion of the Association Manager.
The arrangement was removed due to two main reasons:
It was not fair or consistent, especially when we were insisting that new associations strictly observed the prominence requirements.
There were some examples of some summits with only a few metres of prominence being listed - including some instances where it was possible to stand in one place and be in the activation zone of two different summits at the same time!
Everything is now fair, consistent, and in accordance with the same General Rules. There are probably still examples where things need cleaning up, but we are gradually working our way through these issues.