1668 Charles II Crown Die Flaw

In about 1992 I bought a 1668 crown of Charles II (left in the picture; I'll call this 1668A). Knowing little about milled coins at the time I did not notice for several years that there is a significant die flaw at 9 o'clock on the reverse. When I did I reasoned there must be others but it took years to find one. They are very unusual but the state of the flaw is always advanced. This suggests to me that the die started breaking up very quickly, because I have yet to see one with the flaw in an early state. It crosses the crown and affects letters on either side. I recently acquired another example (on the right in the picture, which I'll call 1668B). This 'new' one also has a serious flan flaw just below the 16 in the date. Only when the coin arrived did I realize that my original 1668A coin has a patch of light abrasion under the 16 exactly corresponding to the flan flaw on 1668B (very hard to see in photos but it is undoubtedly there). This suggests that whatever caused the flan flaw also damaged the die at that point. I've also noticed that the obverse dies are linked too, indicated by the small blob of metal above the king's laurel weath at about 1 o'clock. Another example can be seen at: https://collections.tepapa.govt.nz/object/107023.

I have also seen examples of this obverse die paired with an undamaged (different) reverse die. From this I'd surmise that when the damaged reverse was noticed, it was discarded and a new one loaded.

So, my question is: has anyone else seen a coin with this 9 o'clock reverse flaw, and has anyone seen one with the flaw in an early state? The famous 1658 Cromwell crown flaw can be seen progressing across various coins as the die degraded. There must have been a period when the flaw became worse. However, I've never found anything written about this flaw; milled coins often have minor flaws but this instance is far more conspicuous than most of them.