In my realm server, we are searching for water monuments and woodland mansions. We acquired one of each maps from a local cartographer and explored BOTH the woodland mansion and water monument.
After exploring them, we found a new cartographer, traded them up to sell the explorer maps, and bought the maps. They reveal the same maps from the previous cartographer, however their maps are unexplored.
If we buy a map from the first cartographer, we get the same map with the areas where we have been revealed on the map. Buying a map from a second cartographer reveals the same map, but completely unexplored.
This can be seen in the provided screenshots of a local woodland mansion and water monument. One map shows a partially explored map proving that we have been to the location. The other map shows the same location, unexplored, bought from a cartographer after exploring the first map.