I’ve never heard to term “lassie error” before, but I like it – it’s both evocative and descriptive.
You are not Ken Thompson, 1973 is a long time gone, and all the cost gradients around error reporting have changed. If you ever hear this term used about one of your error messages, you have screwed up. You should immediately apologize to the person who used it and correct your mistake.
I really like the idea of providing discrete error codes for every error. It’s an easy way to share and discuss errors.