Yes, on some 'multiple mark' types, Airfix tend to use a common sprue, so you may find an extra, different canopy, or rockets and bombs for instance, where it's not needed on the particular type being built.
Well it is 'Spitfire Season', with the BoB 75th Anniversary !
Picked up the 'Ventura' RAF serial number decals from my neighbour's shop, where they'd been left yesterday, and also the first volume of the 'Battle of Britain' archive - at first glance, a truly excellent companion series to the 'Luftwaffe Crash Archive'.