Could someone be so kind to help me understand this profiler's information:

HUDSON, ANDREW Pvt - Enl 25 Jan 1863 at Little Rock, AR. Deserted 10 Sep 1862. Took oath at Little Rock, AR 2 May 1864. Ht 6' , eyes gray, hair black, complx drk, residence Pike Co, AR.

I understand the enlistment date but I am not sure as to why the date on desertion is before the enlistment date, and what do this mean in the next sentence "took oath" in 1864?

Thanks,
Matt Friend