A No. 4 Mk1/2 is a modified No 4 Mk 1 (no star) that has had the receiver modified to accept the hung trigger from the receiver, instead of the trigger housing.
A No. 4 Mk1/3 is a former No. 4 MK1*
These rifles that are in circulation right now are by far the best buy going in Enfields; these will be the good old days in a few years.