Thanks for your investigation, and I'm with you, we didn't get an answer about "why" it's supposed to look that way. The way the surround is affixed to the cone looks very different though (the cone making a roll before the actual surround in the B version), and could be the reason behind this "by design" fibre breakup.OK so if I understand correctly the LF driver comes off the production line looking exactly like the one in the OP (even before it is installed in a monitor), with the rough ridges in the diaphragm.
I found this video where at 2:58 we get a glimpse of a bunch of what look like 8331A racetrack drivers:
View attachment 163889
A few seconds later we see a close-up of a bigger racetrack drive, probably 8351A as it doesn't have the rubber surround with the corrugated sides:
View attachment 163890
In both of these images the diaphragm doesn't have the rough area, in fact, it looks perfectly smooth all around, unlike the driver in the original post:
View attachment 163817
I'm having trouble understanding why the top and bottom parts of the perimeter would have the rough finish, but not the sides. I still see cracked paper, sorry. If other parts of the perimeter can be smooth, I really don't see why the top and bottom can't be smooth. The diaphragm is a wet-pressed moulded pulp component. I am 99.999% sure the mould is perfectly smooth at that spot and so when the diaphragm comes out of the mould it is also perfectly smooth all around. I have seen plenty of wet-pressed moulded pulp packaging that has very intricate details and the finish is exceedingly smooth.
Also, the rough area seems to be angled in a way that follows the shape of the the diaphragm slope (see angled white lines in above image) and it only affects about 80% of the length of the top and bottom parts, respectively, which suggest a mechanical correlation between the tears the geometry of the diaphragm. I understand that the rubber surround is supposed to be the bit that flexes while the diaphragm is stiff and ideally doesn't deform; however, in this particular case, it appears the diaphragm is in fact flexing more than it should under a cyclic load which causes the tears.
I get what said about accelerated lifetime testing, and I believe it is a reliable way to test if properly implemented. I used to work in test development myself. I just have trouble believing the racetrack drivers are assembled with the tears in the paper.
I still think a picture speaks a thousand words and the best way to settle this and prove me wrong (which I would be infinitely grateful for) is to show us a picture of several brand-new and unused 8351B racetrack drivers from the assembly facility. If they have the micro tears like the one in the OP I will have made an ass of myself but I will also be able to put my mind at rest and order a pair of 8351Bs + subs, which was my original intention and the one I would like to go with. If, on the other hand, the brand-new drivers are smooth, then perhaps they might need reviewing, which is fine by me because these monitors are out of stock everywhere and I will have to wait till spring 2022 to buy anyway.
Sorry to be such a huge and persistent pain!