The Beinecke Library has published the Plath Family Papers finding aid .   There is, as can be imagined, a lot to unpack with the finding aid and a cursory review of it also indicates that there are things within it that need to be cleaned up and corrected.  But it is an enticing textual and organizational look at the papers that comprise this part of the collection. There is an "Addition" as well but that finding aid is not yet live. When it is live, this link will appear here. There are many letters from Plath to various people which is exciting. These include, without a doubt, the original letters Plath sent to her brother Warren. The Lilly Library has copies. The letters to Mrs. Plath are itemized, but those to her brother are not (at the time of writing). So it is unclear at the moment if there are more letters. Researchers will be able to access the collection in the first week of December. Undoubtedly there will be much more to discuss in time.  In case you mi...