pre flight dining / supper (or whatever BA call it) is indeed restricted to those flying in CW. A shiny card doth butter no parsnips. Same as e.g. JFK as well otherwise it's just snacks and whatever other food - sanwiches etc - is available. This is not a new thing but often confuses.
The IAD BA lounge is only PP between 7am and 2pm. It becomes BA only from 2.30