I've been competing with Leupold scopes for over 10 years now. Since the evolution of the Mark 4 series, the VariXIII series were matte finished and then they expanded the VariXIII line to accomodate the 30mm tubes and used the target knobs with the 3 x 1/16" set screws.
Then they started calling the 3.5 X 10 x 40mm version "Tactical" back in (can't quite remember now) 1998?? Afterwards this model was renamed the Mark4 PR , as well as the VariXII 3 x 9 x 40mm, that became a Mark4 PR , too.
Help me out here if my information is not accurate.
It seems that the Mark4 M1 and M3 (different knobs entirely) have become the LR/T series or MR/T series.
My best guess is that it's all about the marketing end of things, the rebranding, I mean. I compete with Leupolds on my operational sniper rig, my counter-sniper rig (building a 6.5 x 284) and my Service rifle rig. All of them are either LR/T or MR/T versions. yeeeeeha....
Hope this helps,
Barney