You might enjoy reading Dave Hitchon's (FB's) report.
He may have been the racer at the event with the most years of AR under his belt, and he has also designed courses. In his report, he made some comments about how he worked with those trails/roads based on his past experience with the reliability of such manmade features.
Because the map was based on 1988 info (I think U.S. map data is usually newer?), some of the snowmobile trails have been re-routed, and some of the logged areas no longer have trucks passing through. Mother Nature takes over surprisingly quickly, as you noticed. (Good on you for realizing that smaller trees and ferns could be an old road!) Conversely, there are new trails and roads that have been built since the map was made. So an orange line may be useful and it may *not* be useful since a lot can change in 25 years. Generally, it's safer to work with water features and contours up here when you can, and if a minor mapped road doesn't seem to have a purpose (e.g. an obvious destination), be particularly suspicious of it.
In Bob's races, some of the most reliable trails are the bold black dashed lines that he adds manually because those are based on recent GPS tracks from our course testing.