I think this has been brought up briefly before, but I wanted to give this issue its own topic. In entry
2573910, I've suggested adding a note saying the expressions とんでもありません and とんでもございません are considered incorrect and that a different form is preferred. This note is about the very construction itself (just like some of our partial ateji-notes) so therefore applies for all 3 senses, despite being inside of just the first one. Normally we don't duplicate these notes but instead hope it's obvious as to what the intended message is, but in many cases, like in this, I think there's an unfortunate amount of ambiguity left in there. I think there's plenty of entries where this holds true, esp. when the note is a comment on the reading or the kanji.