I let my local dealer (in Germany) where I bought my two 600s send them in to Canon. Took about two weeks until they were back at the store. At least if the date that the shop claimed to have notified me is correct. Likely some mistyped email address, but I never received the notice and in total waited about 6 weeks until I went to the shop to ask. I'm not currently qualifying for CPS, otherwise I would likely have sent them in myself for priority service.
I got the same devices back (same serial numbers) and both now have a white dot (hope Canon really did more than make the white dots…).
BTW: While I did some tests with the returned flashes, I noticed that when I trigger them with my Yongnuo Speedlite Transmitter YN-E3-RT, they recharge faster than when I press the test button directly on the flash or remote trigger them with the other 600 or the 430III. When I take images, with the YN-E3-RT the light output seems to be very slightly reduced (1/10 of a stop or so, reducing power by 1/3 of a stop has a much bigger effect). Also while recharging normally they make some slight noise half way through the recharge, which they do not do with the Yongnuo. Not sure if this was already the case before sending them in, but has anybody else noticed something like this?