Who are the enlists?

I am CantrellxColin

Enlists is the lowest group of ranks in the army which includes ranks:

¥-----------Enlisted-----------¥
E-0 - Recruit
----------------------------------

E-1 - Private [PV1]
E-2 - Private [PV2]
E-3 - Private First Class [PFC]
E-4 - Specialist [SPC]
E-4 - Corporal [CPL]
E-5 - Sergeant [SGT]
E-6 - Staff Sergeant [SSG]
E-7 - Sergeant First Class [SFC]
E-8 - Master Sergeant [MSG]
E-8 - First Sergeant [1SG]
E-9 - Sergeant Major [SGM]
E-9 - Command Sgt Major [CSM]
¥-----------------------------¥

The enlists job is to recruit new members in the front row. And listen to higher ranks.

I'm a bit confused why there is more then one number for each rank.

Ex. E-9 SGM
E-9 CSM