@Buzzbox, well it has appeared on my licence as a combined A330/A350 rating, but I have never yet set foot in the latter, nor done a differences course.
@uxb99 Because a cover or a pin on the flight deck does not prove that the aircraft is ready to fly - another cover or pin might have been fitted to the aircraft. Those who turn round to look at the cover and pin storage on the flight-deck to confirm covers and pins removed are setting themselves up for a massive fail one day. The actual aircraft needs to be checked externally.