Although the Wallace Correspondence Project (WCP) has been running for 6.5 years and we regularly search online catalogues of archives around the world (as well as auctions and private collections) for letters and other manuscripts new to us, we keep on finding new items all the time and I sometimes wonder whether we will ever discover all or even most of them! I guess the answer is provided by the Darwin Correspondence Project, which has been running for more than 40 years and has many more staff than we do. Even after all this time and with so much personpower, they are still finding about 50 'new' letters a year!
Since Phase 2 of the WCP began (in December 2017) we have found more than 500 'new' letters - about the number which are published in one of the thick volumes of the Darwin Correspondence. These turn up in all sorts of places - recently I found one in the Wellcome Library Archives which had either been overlooked by us, or had been added to their database since we last checked. Yesterday I found three in the British Newspaper Archive - and we have just begun to check this resource, so who knows how many we might find there. Today our full-time Researcher Matt found a very interesting letter in the Asa Gray Correspondence file in the Gray Herbarium of Harvard Library - see https://iiif.lib.harvard.edu/manifests/view/drs:49797987$317i. We had overlooked it previously because it was a letter we thought we already had from the British Library. Matt realised that although we had the final version which Gray had sent to Wallace in 1880, the document in the herbarium was actually a draft version with different wording to the final one. Matt writes that in the letter "Gray was complaining to Wallace that one of his lectures wasn't cited in chapter 7 of Wallace's book Island Life. The version sent to Wallace was worded in a slightly more diplomatic and indirect manner. For example:
"The close of your Chapt. VII. p. 119,120, would so completely serve for an abstract of the report of a published lecture of mine which you did me the favor to commend that I should have been pleased if you had referred to it upon this occasion."
"The close of your Chapt. VII. pp. 119, 129. would so completely serve as an abstract of the gist of a published lecture of mine, which you once did the honour to commend, that I should have been pleased if the coincidence of view had been referred to."