Sometime in the area of 2008/9 the exhaust brake function , went from being provided by a separate system to being an internal function of the turbo. I'll see if I can track that date down , with info on the turbo, that's when it became standard . I retired from Dodge/Cummins service work in 07 and didn't keep up on all the changes.
EDIT: Made it back in time to edit.
Starting with 2007 1/2 and the 6.7 Cummins, the integrated VGT exhaust brake, became standard.
And I see , timetogo , already said this , acronym MY = Model Year