Thanks for the interesting article. I have just been looking in the book "Residuals and Influence in Regression" by Cook and Weisberg (1982) who discuss some of the benefits that Sherman-Morrison offers in a regression diagnostic context. Interestingly in the appendix on updating formula, they give first credit to Gauss for "a version of" the rank-1 update formula. They give a citation from 1821 in case you are interested (written in Latin).