The book is split into a main section and appendix.
The appendix (which my Gt Grandfather is in) describes itself as listing "Names of Men who have attested under the Group System".
On the other hand the main body seems to refer to those who have joined-up as it gives their regiment and unit.
So unfortunately not quite as clear cut.
I have just finished going through the Ancestry military records by matching these where possible to the index cards and I ruled out anyone who actually joined prior to the Derby Scheme and anyone else who I could clearly identify as not being my ancestor.#
This leaves five possibilities as follows:
Dillon, Charles. Corps: Manchester Regiment. Regiment No: 302946. Rank: Private.
Dillon, Charles. Corps: Nottinghamshire and Derbyshire Regiment. Regiment No: 306529. Rank: Private....
Dillon, Charles. Corps: Royal Army Medical Corps. Regiment No: 31662. Rank: Private.
Dillon, Charles. Corps: Royal Field Artillery. Regiment No: 2720. Rank: Driver.
Dillon, Charles. Corps: Royal Scots. Regiment No: 45773. Rank: Private.
From this it does indeed seem probable but not certain that the Manchester Regiment Charles is my ancestor. I will see if I can research the service numbers perhaps to try and rule any out for being too early?