I wouldn't say common, but it does happen. It's usually the problem in the end and you can't pass the OCLT, the water is crystal clear, zero CC's. That's when to start checking for algae hiding places. Lots of times a member will bring it up during somebody's SLAM to not forget to check that out like was done in your case.
To put that in writing in the SLAM Process article would have to be taken up at the next board meeting with upper management ! I'm just a grunt. Lol