Leupold M5 turret question

[chad44]

Why are some mark4s equip with the m5 turret that has a button in the center and a revolution indicator and others look like the classic older mark 4 turrets but have a m5 stamped on them. How can a guy ensure he gets the newer turret?

 

[Target07]

It is my understanding that the standard M5 turret is on the 30mm maintube Mark 4. The locking turret, also known as the "M5A2" Turret, is only on the 34mm maintube Mark 4 scopes.

I believe this is correct. If not, someone correct me.