Trust me look at the v3 thread there are plenty of black models with the issue.
The v3 and v4 dial are completely the same they only changed the printing and the dw. Same with blue and white and grey.
I saw hundreds of QC pics you can believe me on that. It's also a batch thing some look worse than others. They "burn" in the stamp that's why you have the valley.
Edit: it's also present on your picture in the middle. It's just harder to spot on black.
I'll take your word for it as you probably have seen more than me. But even looking through the V3 thread I am seeing a vast majority of V3 blacks without a valley (or maybe a very narrow one in pictures, could still be because of lighting) whereas there are zero non-valley blue's (I cant say anything for white and grey as I have not looked). I cant even find a definitive V3 black with a valley as pronounced as the V2J blues.
I still don't believe there is a valley in my last photo, you must be seeing the light shine off the raised edge of the textbox above "AUDE".
Maybe in the V4, they got their tooling dialed in and got valleys consistently now.
Either way, I would have preferred no valley for all versions as that is closer to gen.