Actually . . . as you know, we allow later Colt and S&W revolvers in liu of the originals, due to rarity and fragility. Thus the Army Special/Official Police is allowed in place of the New Army and Navy, and a fixed sight, round butt, blued K-frame is allowed in place of the M1899 S&W. Both these guns are nearly identical in appearance and function to the older weapons. So also we allow the MK IV .380 to be used in place of the earlier MKIII .380, (In appropriate portrayals) as it is nearly identical in form and function to the earlier revolver, in it's target gripped form. MK III production goes back to 1896, with the appropriate square butt target grips available even then.
Unfortunately, this is limited for the .455 models. The MK V can be used in the Victorian match, but not the MK VI, due to grip configuration, I don't believe a square target grip for the large bores was introduced until 1905 or so, though I would be glad to be corrected in any of this if I am wrong?