I've been confused by all the add-ons and expansions in the Simbin Race 07 series. A while back I found a few posts on the nogripracing forum that helped with this. I did a quick search this morn and found probably the most helpful;
Which expansion to obtain? I'd bought a Race 07 & GTR Evo package and then picked up a few single expansions off Steam so I think I have most of the expansions in Race Injection...GT Power, Retro, STCC2. I picked them up whenever they went on sale, so not a huge cost.
I do not have the Race On expansion which apparently includes some iconic American tracks.
I hope the url to the forum works and the info is helpful,
Regards,
Derek