Is my old license valid for 6108R?

Short answer: Yes!

If you - at any point - bought a license for Aventurin{e}, then this existing license is still valid for and usable with Aventurin{e} 6108R. The only exceptions being those licenses that were revoked due to refunds or when replacement licenses were issued during license upgrades. In these cases we might have invalidated the returned licenses so that only the newest one was still valid.