I have about 1000 miles on my 818 with the donor ball joints that came with the donor front lower control arms (LCAs). I replaced them with some Moog ball joints yesterday, and cut off the boots to inspect the old joints for wear. I'm happy to report that there is no visible sign of wear. Here's a picture with the boot and most of the grease removed.
I swiveled the ball around and could not find any wear marks or any sign of looseness in the joint. I will cut one open to make certain the cup is in good shape too, but based on how smooth and tight it is, I don't expect any surprises.
Considering the critical role theses joints play in holding up the car, I plan to replace them annually. I will post the status of the joints again when I swap in a new set in a year.