FWIW, on LHR-SEA I've never had the dessert with the salad on the same plate. It's always:
- Appetizer and salad
- Main
- Dessert
They've always brought out the tray with the appetizer and salad, and then left the tray between the rest of the courses. When they still had the chocolates on the tray, they would be there with the appetizer and salad.