I know the D&M had formerly only gone to Cheboygan via the Lakeshore route. They gain control of the PC line up the middle of the state and moved operations to this line, leaving the operations between Calcite and Cheboygan very sparse.
The D&M took over operations of the line from Cheboygan to Mackinaw City at this time as well correct, including the ferry.
MIGN took control of the lines from Mackinaw City to GR correct? This included traffic brought off the boat in Mackinaw by the D&M. What amount of traffic went each directions from the Chief out of Mackinaw? Everything I've heard seems to say the traffic went via the MIGN. Would it have been easier and cheaper for the MIGN to have switched the Chief instead?