The MK1 has the plastic trigger blade which was later changed for alloy.MK11 have the alloy trigger blade & slotted safety catch.

Early MK1 has a palm swell later stocks are not as well pronounced,it also has the slotted barrel for the wrap around foresight later it was dovetailed.Three foresight types over the years.
Some MK11's have the wider panel checkering on the stock,the ASI imported model had Series MK11 on the breach.

Beeman models are stamped on the right hand side of the cylinder.

The Deluxe Sport came with opens which is the most common & the Target had a peep sight & foresight with different elements.

Manchester Air Rifles had approx 50 with factory Walnut stocks.

The most rare is the .20 version prototype around 3 or so made.

Butt pads are slightly different around 3 types across the years but don't seem year specific apart from the early red shaded type,later ones look to be the same as HW with out the branding.