I'm not so sure. If I load a saved map in Google Maps (e.g. someone has saved a route with markers and shared it with me), and then I go offline whilst viewing it, Google Maps on Android will show an error after a while and I'll lose the route and markers entirely. This occurs even if I've marked the area as an offline map. I guess it's just a case that they treat the saved routes in a different way. But it's really annoying for my use case (which is finding crewing points for long distance running events in the middle of nowhere with no mobile coverage).