I'm not trying to flame or anything but, most games featuring Army ranks usually go Private 1st class> Specialist> Corporal, While Corporal and Specialist are equal in pay, going from Specialist to Corporal is a lateral promotion which is usually only temporary. There are 3 ranks to Petty Officers the lowest being equivalent to Corporals. I do agree on the dropping of the "Third Class" from the private tier though. But anyways it's Eorzea and the rank names and trees are up to SE and their imagination, maybe the GCs mock the ranks of the Empires collective armed services which results in the hodgepodge.