It's my understanding that the original sticker rule was written with non-project stickers in mind.
That being said, the profile does operate within the Notables project guidelines, so it's something that "should" remain on the profile. Because there are so many Notables profiles within the project, it is impossible for the team to constantly hunt and restore project boxes and stickers to profiles, so there are going to be situations like this that pass under the radar. However, because the profile meets the project conditions, another PM could come along tomorrow, see that it's missing, and restore it without questioning why it was missing. And then another could remove it. And another restore it. The reality is that it is going to be easier in the end to keep key project stickers on profiles than it would be to go out and remove them.
The other aspect of this is if a Magna Carta Baron that fit the project was encountered that had only a Notables Project box and no MCB sticker or project box. I strongly suspect that no one would think twice to add that project box to the profile, since it fits well within that project. I would also hope that at the same time, one would not then remove all other project boxes to simply eliminate them.
Notables also serves as a key search criteria by a number of PM's, so by removing it from those searches, it impacts PM's efforts to find key profiles. If we reach a point where we agree to disagree about the stickers (and I would hope that is not the case), then I would think it would be suitable to manually add the category to these profiles to continue to enable the search capability (which is essentially what the sticker accomplishes).