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I had lots of little ones where a 'road' I'd picked was a farm track or whatever - in which case I'd just zoom out, ride around it and hope for the best - trying to get back onto my route asap.
People who spent more time route checking probably don't have this issue. I hate maps, routes, navigation, etc so I will always be ad-hoc routing and never know where I am. I'm ok with that.
I didn't have to do any really big re-routes and had offline maps in the form of Google and OSMAnd. In the end I mostly used 1000 with RWGPS coming into plan after 'swimming' across Montenegro.