The "1951 Models" are divided into three categories, denoted here 1 to 3 and represented by a single variant. The "Waffenkontrolle" stamp is the same for each variant.
The blade now has a vintage mark showing the last two digits of the year (e.g. 51 for 1951).
PDF document, a copy of the plan for the Model 1951 soldier’ knife
Warning : There are civilian replicas of “1951 Models”, for example Victorinox kives with the reference "151 R". These replicas should not be confused with the soldier’s knife !