I’m putting H.A.'s letter at the top of each of these, sorry to anyone who wants to poke at all the puzzles.
Last year, I sent a box to Saberlane that seemed to have a magiqal past to it (seen here).
I made the foolish mistake of not copying the letters inside before sending, and two of them were lost after Sabes sent them off to other Mounties to solve.
Imagine my surprise when, while organizing my digital files, I came across a document I didn’t recognize.
It was a copy of the seven letters, and the numbers on six of them were different than before.
Here’s the less-puzzling of the seven letters:
Through one of our mutual acquaintances, Mercy came to access what the men seem to be calling the All-Seeing Eye. Knowing it for what it was, she sent it on to me in her last correspondence, believing someone of my House would know best what to ask.
When the Eye opened to me, it told me of Hope for the fight in which our mundane brethren are embroiled. As for the second request, a far future was Illuminated. One where our Houses no longer have need to meet in secret betwixt one another as we do now.
It is with these descendents in mind that we leave these messages. Each of our secret group has written a small note, twice-encoded to keep others in our respective Houses from stopping us, addressed to our future counterparts. To my knowledge, none of them contain any Earth-shattering information about our Houses, just a short greeting from each of us.
The Eye granted me the two cyphers used, and left with a clue to decrypt it.
The book will Guide you to play fair.
It means nothing to me, but it may to you.
Until your time comes, we shall continue to protect It, even from one another.
Faithfully Yours,
H.A.
And here’s the letter that was labeled “Flints” (I had to screenshot it, pasting the contents wasn’t working 
)
7/16: So, a couple of the numbers changed… Here’s a new screenshot? I’ll let you know if there are any more as the rest is poked at.
7/17: …yep, 'nother number changed.