I've always experienced that OEM bars only fit a certain set of cars (For example the Mk4 Jetta roof bars only fit the Mk4 series of Jettas)
Other than aftermarket (Thule and Yakima etc) you can't get bars to fit different eras of car - and you may still need to purchase the fitment kit.
So far i have seen that Thule has a kit that seem to fit an assortment of roof bar equipped vehicles. I use the Thule Aeroblade and the 450 Crossroad foots which affix to the stock roof rails.
However, the rails on a 2015 Q7 are flush so the 450R crossroads mounts don't work (you need the 460R pillars.
In either case the base bars can be used between the Touareg and Q7 but you need a different set of pillar/rail mounts for both vehicles.
Not the one choice for both.
In my case - I can share the bars between Jetta and Touareg BUT I need to use different adapters for either car. (cost was about $250 versus buying a whole new setup at $600)