REST stands for Representational State Transfer, so http status code has business meaning to the "state" itself. 404 is not ambigous. The real ambiguity is from

REST stands for Representational State Transfer, so http status code has business meaning to the "state" itself. 404 is not ambigous. The real ambiguity is from 404, 400, 422 errors that you choose to return based on your validation logic.