John Wesley Joiner did not have any prior service. The term "enlisted as a corporal" is a little misleading. The way it normally worked in the Provisional Army of the Confederate States was that a group of volunteers from a certain area organized a company, and elected a captain and three lieutenants. The captain then appointed a non-commissioned staff (usually five sergeants and four corporals). Thus organized, the company was mustered into the service of the Confederate States for a specified period of time. This is the enlistment date. John Wesley Joiner had been appointed second corporal when the company was organized, and held that rank when the company was mustered into service; hence, he "enlisted as a corporal."

The date that the company was organized was not normally noted in the Compiled Service Records. That date can sometimes be determined from other, non-official sources. The enlistment or muster-in date was the baseline for pay, seniority, etc.

I hope this helps.