another way to look at it is comparing it to a mother plant. Every clone you take off that plant is theoreticly as old as the mother it came from, which is why they can be put into flower right after they take root. So do mother plants lose their potency over time... i dont think so. One of the main reasons people get rid of mother plants is because they have outgrown their home. But even when the mother plants are put into flower, their replacements are usually a clone off the mother itself. So again you have a plant of the same age continuing to grow.
So find someone who has kept a strain going for a long time and see if they can remember if the weed they first got was better than it is now. Chances are they cant remember since its prolly been some kick ass weed the whole time.
As far as reveging plants outside after they flower.. well they do it in spain. The climate has to be just right, if your winters involve snow i dont think shell make it. Ive done it indoors a few times, but the problems you run into is the roots. Youll have to trim them and repot like a bansi. Also it takes 2 weeks or more to even revert to veg