I don't think there is any significance in the V1 vs VI marking. Just typing issue as Parabola says. I just received a box yesterday made in 1961 marked: 303" BRITISH (MARK 6z TYPE) CARTRIDGES. They are Metal Covered Solid Bullet 215 GRNs. No reference at all to roman numerals. Along with that box I received another made in 1963 which again all 303" BRITISH CARTRIDGES that are Metal Covered Soft Point Bullets 215 GRNs, with no reference at all to any Mark number.