User blog comment:Xilinoc/Ch. 632 - friend 2/@comment-8669536-20150625095618/@comment-5551986-20150701090836

Yeah. You're right, he could have mustered some at the time, like letters N,B,H etc and left some for the future. But he can see the future so to speak so he would know when and where the remaining ritter are he could have thought "right letter U will be born in 1808, come of age at 1839 and I'll recruit them in 1840" as a hypothetical example, and lets face it, yeah they might not have had technology. Äs Nödt was an oversight on my part, and Yhwach with mutton chops came to see him recently seemingly, you are right they wouldn't have had that tech. *All* the SR was an exaggeration, what I implied was there were no previous ones.

I'm still holding onto a theory that only certain people can recieve the letters because they fill a certain criteria with their own souls and I believe they are based on the state of their own soul. Basically, there can only be one with a unique letter meaning there cannot be a simple replacement otherwise they could have been replaced, which sparked my theory as to why their abilities received from the letter are amplifications of their own powers and potential thanks to Yhwach its hard to explain I can go into more detail but I wont.

Besides the technological argument you stated was a good one but lets face it, its Bleach, it doesn't really follow rules here, the Quincy from 1000 years ago are wearing SS suits and stuff with hats. Unless its made of Reishi you need a machine or a very very skilled tailor from the future to make them.