I really like this site, which explains a little more about H57: http://www.michiganhighways.org/listing ... 6-H63.html
I didn't read it in great detail, but it looks like at least a portion of Brevort Lake Rd is H57, which is all or mostly unsigned and corresponds to a forest service road or former forest service road.
It also appears on the "official" state map
, so it looks like Brevort Lake Rd in its entirety based on that.
Did MDOT spell "Brevort" wrong, or does the lake actually have two O's (Brevoort)?