That doesn't sound right a session should only list items used specifically in the session, that includes Rules, Drivers, Driver Commands, Locos, Consists, commodities and the Route asset. If it's listing stuff that is already in the Route it sounds like at some point the Route was merged with the Session easily done since the Unified Driver Surveyor appeared, I avoid editing the session from driver, avoids things ending up on the wrong layers. Simple Example is say adding a Tree in editing the session from driver will put the Tree on the session layer unless you look at it's properties and change to the route layer before saving. It would help if there was an indication as to what layer you are editing rather than having to have to check in the layers tab.
If all the assets used are on the DLS? from the sound of it they might not be all you need to transfer is the Session cdp and the Route cdp, the rest can be downloaded from the DLS, effectively that is everything that has an upload date in Manage Content that isn't builtin Packaged Payware or Base, Package and payware must be downloaded again from the Content Store to ensure it's compatible with the version of Trainz being used.
Stuff not on the DLS but from third party sites will normally show as locally modified and not have an upload date. In which case if transferring to another user all you need is the Route and session cdps and a cdp just containing the non DLS items.
Third party is another option that can be stuff that hasn't fully gone through the DLS process or assets that have failed the DLS validations and is on the Faulty asset list and require repairing by the Content Repair Group, often they still work perfectly well and ended up on the list because of out of date config, config typos or the dependencies hadn't been uploaded first, thus fails the validation due to missing assets, Routes seem to be exempt from this problem though at the moment. I'm the Content Repair Group Co-ordinator by the way. Unknown assets are also often on the repair list and right click download this version will often but not always find them and download as third party.
