I don't see why this has to be the case. Compare N21 with Cypress (old 5000 series) which had XT, PRO, and LE that were the 5870, 5850, and 5830 respectively.
If you look at those cards compared to N21 the similarities are eerie. Cypress had 3 bins with 100/90/70 percent of hardware enabled. Navi21 is 100/90/75. The price spread for Cypress was 100/68/63 percent relative to full die cost. N21 is 100/65/58 which is similar.
AMD hasn't a die with 4 bins (I'm excluding refreshes where the same die on a much mature process was given a new designation like Tahiti Pro2) since RV770, which is a decade ago. It may be possible that no 4th bin exists at all. The TSMC 7nm is reported as being quite mature and having a low defect rate relative to other processes at this point in its lifecycle, so an even more cutdown die feels a little less likely.
Maybe we eventually do see something that's a lowest common denominator salvage die, but it would have to be something with reduced memory controllers or infinity cache or a disabled shader engine because it's hard to imagine too many of those existing and at some point the bin is bad enough that even a high clock N22 will come close to it. If the yields are good enough maybe that part is so rare that AMD just scraps them or saves them for some special OEM-only part.