Ed, I'm not sure that I'm on the right track here, but I think your 100th Regiment might be the one described here: https://books.google.com.au/books?id=uQt4PleGb8QC&pg=PA249&dq=%22daniel+sedd on%22&hl=en&sa=X&ei=3Q87VZe2IYaJ8QXevoGoDg&ved=0CEcQ6AEwCA#v=onepage&q=%22da niel%20seddon%22&f=false page 249 onwards under the section headed "448 Major-General Daniel Seddon." The others of interest (101, 102) are briefly listed at http://wiki.fibis.org/index.php/101st_-_109th_Regiments_of_Foot_-_Lineage and it appears as though they were disbanded in 1783.