You have put it very well.

What I love about the letters along with other things is, that sometimes we can see where certain things in her books are coming from.

Though I confess I have sometimes been absolutely lost where names are concerned, but gradually they are beginning to fall in place due to the GR.
And best of all is understanding them, and having things make a lot of sense with Julie's marvellous assistance in making reading her letters as fascinating as reading her novels.

Though it would have been great to have had *all* her letters, I agree with you that what we have is valuable treasure indeed.