This was my experience:
I bought 4 new wheels, 4 new tires. They were all balanced using the "standard" method. (Not sure if static or dynamic, guessing static.) They were mounted and I had a vibration that occurred at 60-65 mph, only on acceleration.
Since everything was new, I could get away with mix-matching tires to the front to get the least amount of vibration possible. After a few tries, I finally found an acceptable combination. So then I had 2 pretty good tires in front, 2 really bad tires in rear.
11,000 miles later, they were to be rotated again. (A little late, it slipped my mind.) I took them to the same place that did the mounting/balancing before, and requested that the rears, which I KNEW were bad before, be "Road Force" tested and balanced when rotated.
The diagnosis: both were almost perfectly balanced. The owner did it himself and said both were about a 13, a well balanced tire being 15, as a rule of thumb. I don't know what those numbers mean, and didn't ask. I should have had him test the former front tires, but $$$.
So he didn't re-balance a thing, and just rotated the tires normally. I was confident the vibration would still be there. I tested it on my 30 minute drive home and, lo and behold, the "bad" tires were COMPLETELY vibration free!
Everything was tightened down the same and torqued the same as before, the only thing that changed was 11,000 miles on the tires. Explain that.