That is correct, the Mk1 has the 25mm leather seal then later on around early eighties it had the synthetic seal up until the new 99/50 came along with the 26mm seal.Hope that helps clarify a little.
The MK1 stock has no but pad & finger grove on the fore end ,it has the fixed post fore sight & early version of the rear sight, the later synthetic version has the modern sights & stock.