It's nice to respond to someone who has actually done research before blindly posting a question on a travel forum so I hope you find what you are looking for.
The best way to get a response from a tourist office is to actually call them and many employees will speak some if not very good English. I would tend to think that trails maintained by the communes (that aren't designated GR trails) wouldn't be shown on the map but I could be wrong. The dotted lines are noted as the boundaries for communes and the dashed lines are the walking trails, if that helps. The IGN maps do have legends and I'm looking at one of mine for a scale 1:100,000 map. Try googling the phrase 'randonées dordogne' or 'cartes randonées dordogne' and you'll get lots of hits for sites about hiking in that area, sch as this one: There are other resources on-line for hiking in the Dordogne but you'll probably need to be able to read French, although google translate should give you some rough if not slightly awkward translations. You can even get more detail with the 1:12,000 maps. I'm assuming you've found the website where you can buy the IGN maps on-line and the scale 1:25,000 are good maps.
