Some of info is same in each book but Herb Russ added and corrected info in each volume and sometimes referred reader to a different volume for more info.
I contacted Herb after he published Volume II with info on my family which led him to change info in Vol. III for several Jonathan Russes, one born 1762 in Derryfield, NH.As info, Volume II has 435 pages and vol III has 284, not including the indexes for each.I tried to purchase Vol I but no copies were available.
I believe most of the main characters like Sir Thomas Russ in England & his father, who is listed as Reigolde but is actually Reginald, are listed in vol IV.Also, the John Russes who started the American line in 1600 New England are in vol IV.
I have volumes II, III and IV so if you don't see info on your ancestor in Vol IV, let me know if I can help.