Website for the Friends of Bobby Jones
http://friendsofbobbyjonesgolfclub.org./
Reading the history of the club, I see:
1926 - Original Ross 18 opened
1952 - 9 holes added by RB Harris
1967 - 9 holes added by Roy Albert Anderson. At this time the original Ross 18 was divided, with 9 holes paired with each of the newer nines.
1987 - Ron Garl renovation to the American course which includes one of the Ross nines. In the words of the Friends of Bobby Jones Golf Club: "...the work consists of significant revisions to holes No. 10 through 18 of the historic 1925 Donald Ross course, altering the Donald Ross Design Intent..."
So it seems only 9 holes of Ross remain at Bobby Jones.