User blog comment:Xilinoc/Ch. 543 - Letters/@comment-5657895-20130626140553/@comment-11051098-20130626143307

Aside Bazz-B and As Nödt, it was NaNaNa Najahkoop who attacked Yamamoto, not the Luchadore guy, or Mask De Masculine (I guess he's the one you meant).

I guess Yhwach has the letter A because he was the first Quincy. The first Quincy and the first letter makes sense. As for Haschwalth being Stern Ritter B, no surprise. The letters might have been given according to strength, in which case Royd might have beaten Kenpachi because he imitated Yhwach. I don't know.

The "Old Man" must be strong, or at least very quick, as he managed to destroy Kyôraku's eye. But he did attack quickly with no hesitation, and Kyôraku admitted he was caught off-guard.

As for the theory of the Stern Ritter and how they got their powers, you might be onto something. They might have been "granted" power directly from Yhwach, and if so, that might be the reason he called Uryû the "last Quincy alive".