I purchased the Two Strong Pack, GT3 Pack and GT3 Challengers Pack vehicle packages a while ago. I migrated from the Windows 8.1 operating system to Windows 10. After reinstalling rFactor2, the vehicles purchased were not reinstalled.
Whatever you do, don't buy them again. Try this: https://forum.studio-397.com/index.php?threads/missing-dlc-tutorial.62565/
I am saying that I tested all the suggestions contained in the pages of the link https://forum.studio-397.com/index.php?threads/missing-dlc-tutorial.62565/ , but to no avail.