Every time you generate a new track with the same settings it will be different, so if someone else makes one it should be different as well. However if you generate a track online you will be able to return to it any time you want as long as you don't check the "regenerate track" box when you select the theme (Toscana Tarmac for example).
Creating a new course either online or offline will cause you to lose the old track. I'm not sure if this only happens if you make a new track from the same theme, or if generating any new track will cause it to be lost. One way around this is that if you have a friend who was there when you made the track, that person can still pick your old track, at least when in your lounge, until they do something on their own to lose it.
Hope this helps. I haven't done extensive testing beyond that. The only other way I know of to get other people to have the same track as you is to share it.
