I have nothing against using a GPS for a tour, but I have always relied on paper maps.
At the start of each day of a multi day tour, I spread out my maps on a table. On a sheet of paper, I sketch out an anticipated route, including alternatives. I include just enough detail to get me where I hope to get to.
I fold the sheet into an accordion, and slip it into my map holder. As often as needed, I refold my schematic map. If I get disoriented, I pull out the big maps.
I haven't had the experience of discovering that a paper map was out of date, but of course it could happen. But a GPS system may not be foolproof. While driving, Google Maps once led us to the wrong destination. We had to check a ten-year-old paper map to get back on track!