I've not dealt with many wheels, 3 sets from three different bikes. Plus, I check them on my home balancer. It beat Harbor freight quality, but barely. Based on that, one rim from the six total has the heavy spot at the valve stem. The other 5 are at random locations on each.
I do think its close enough to not matter much. Its a fun diy job since a person can get so fanatical about balance, but by the time I start trimming a 10 g weight with a dremel tool.....its just for me.