Complex sentence: However the rank of the appointment holder and the holder's appointment are separate; that is all Lieutenant Colonels are not CO's, and although most COs are Lieutenant Colonels, that is not a requirement of the appointment.
Split into simpler sentences: However the rank of the appointment holder and the holder's appointment are separate. I.e. all Lieutenant Colonel's are not CO's and although most COs are Lieutenant Colonels, that is not a requirement of the appointment.