Ed, What is the evidence? Is it the quality of the strings? Or the skill of the stringer? false beats are a continuing problem.
I wish I knew. After 36 years of this, I am still baffled, at times. Many are easy to remedy, just change the wire. This is the most common source I have found in new, expensive, American made grands, and I wonder if careless stringing and chipping is to blame. I use the same wire and see far, far few problems with false beating. I have seen the factory stringers, and I think they go way too fast to avoid overstressing a significant number of strings from C6 up.
My "evidence" is a number of older pianos that out-sing the new ones. Among them is a 1914 model O that I completely replaced the action in, but left the original stringing. I did this because it sounds better than the new one it is next to in a professor's studio. She prefers the older one to a 2000 model L. The older piano has one or two questionable strings, the new one, dozens. Actually, all new models of this brand have numerous un-tunable strings!
I am told that virtually all steel today has some recycled metal in it, and that contaminants like copper cause wire to be weaker,whereas, in 1914, all the metal was being smelted from virgin iron ore. I am not a metallurgist, so I can be easily led by logic rather than knowledge on this one.
Other false beats go away when I lightly massage the wire against the bridge pin. This is done with a very small hook, right in front of the pin on the speaking length. Others yet are persistent.
Jim Ellis and James Arledge did some research that indicated that a false beat would always occur when the curvature of the music wire aligned at 45 degrees to the hammer's direction. Not against it, or sideways to it, but 45 degrees off of vertical. Hmm. I have gotten rid of one impossible beat by loosening the wire, turning the coil one revolution, and then putting the string(plain wire) back on. I have also had them break when I tried this...
I suppose the best approach to false beats is the most experienced one; give it your best shot, and then continue on. The beginner will spend a lot more time before deciding it's wasted effort than I will !