The Ellen R Rugg Book is indexed by the 10 children of John Rugge Senior.Each of the children have their Descendants listed in order of birth (more or less) when replies to queries were received by Ellen Rugg.In 1911, think 72 years before and that would be the available Census accessible but probably not on microfilm projectors as we have today!
As to the Back book index, these are also by name(s) of each of the Children and if you look at the top of the Index pages, you will see the male heirs, John (1), John Jr (2), Thomas (4), Daniel (9) and Jonathan (10) and not the book title "Descendants of John Rugge!
The numbers before everyone's name is the order of descendant "from John Rugge Senior" which also includes the forebearer after everyone's name!
There are George Rugg's names for Thomas, Daniel and Jonathan where I counted 5 George Ruggs are descendants of Jonathan Rugg.The number of George Ruggs names you found on 577 were for Jonathan Rugg's line.
This would literally make Indices within the major Index so you would have to look for: John Rugge, pg 529 John Rugg Jr, pg 529 Thomas Rugg, (4) pg 533 Hannah Rugg, (6) pg 534 Rebecca Rugg (7) pg 534 Daniel Rugg, (9) bottom 534 Jonathan Rugg, (10) pg 568
THEN if Cornelia Rugg was to be found as #1187, simply search for the number 1187 between descendants numbered 1180 and 1188!She is listed as a child of Samuel, s/o Asa, s/o Reuben, s/o Daniel Sr, S/o John Senior! After each ancestor is their key number to read about their birth, parents names and marriage.
Jean firstname.lastname@example.org A descendant of Daniel Rugg (9), Nathan #655, Elisha #3566, Artemus #4037, HN #4044.