I'm sure you know this, but my guess is that the point being made by having dead female authors "sign" the letter is to demonstrate that it's somehow hurting the legacy of female authors to include a trans woman in their ranks.

I mean, it's a dumb point. Anyway, despite being 100% not really interested in the book (from the description on Amazon) I bought a copy and will read it, because dammit, trans women are women.