Should have said "if it can't appear in the domain, it can't appear in the range". Obviously if it appears in the domain it can also get into the range - a simp

Should have said "if it can't appear in the domain, it can't appear in the range". Obviously if it appears in the domain it can also get into the range - a simpler example with real syntax is \x -> x. What I'm arguing is that anonymous records are unnecessary and it's silly to insist that problems with anonymous records should derail a good solution for concrete ones. But you are right that it's a bit more than just syntactic.