all that work could be stood on its head in a single season.
I worry about that as well but the trick is to hold on to 2 or 3 year old queens which have the right genetics and have mated with the right drones.
If the matings are particularly bad in a given season you would still have some decent queens to graft from in the following season.
If you graft from known genetics your drone colonies should always be ok irrespective of the matings.
I have about half a dozen colonies with a lot of yellow banded bees but all the drones are black. I am 100% confident about the queen these queens were grafted from so they are perfect as drone producers. I would never graft from any of these.