text: Oh, I see - but they throw me off when I look for notes to survey and fix :)
  It would be better to include that in data - for example, you can add a node there with a tag "note=...". This would allow anybody attempting to edit the place to view your comment, while keeping the note map less red.
  For demolished structures or closed amenities the suggested way is to prefix the main tag with "disused:" or so - thus amenity=cafe would become disused:amenity=cafe. If the area in question is large enough and you fear one node with "note" might not be enough, you can leave some tree rows or nodes in place and prefix their main tag, too.