negative surveys without identifying information of any kind (which were incredibly rare)
Not rare at all.
I'm thinking of a restaurant I go to, for instance, that has comment cards with a survey on them. No need to add the Date or Time (although you can, if you wanted to, I suppose). It also has about 5 restaurants that are covered by the one card. The 5 are owned by the same entity.
Seriously, if one less than stellar mark on that thing gets everyone who has ever possibly worked at any of the 5 restaurants a "stern talking to," there's an even more serious problem with the system. I really truly can't believe that they chew out everyone that works at those 5 places at all times of the day or night just because they got some feedback from a customer that has a suggestion on how they might improve.
At this restaurant, as an example, they've taken off a menu item that I used to get every time I went in. I think that the reasoning behind removing it (confirmed by the wait staff) wasn't really thought out fully. And I have a suggestion on how, if they bring it back, they can overcome the problem that they initially had. Yeah, I complete that survey when I go in. And that's at the recommendation of the servers - they want it back as well. If, for no other reason, because they're the ones who are hearing from the customers that they're wanting to order it! If that gets people in trouble, I can't help it. Don't ask for comments if you don't want to hear them!