Yvonne,
The Union POW records were taken from the compiled service records of "Sam Wilbern-Pvt/Sgt"---" cards filed with:
Samuel Wilbourne"-Thompson’s 4th Ark Cav- Co C, CSA

And include such cards as:

3/15/63 Enlisted Roseville
"Belonged to an Infy command when he came to this Co"

[However, there is another card in that group that states he was promoted to 3rd Sgt on 2/28/63 which is before that 3/15/63 enlistment date that is shown. That alone should make that enlistment date suspicious][Also, there is yet another card in that group that states "Enlisted 6/20/62 Roseville"]

The so called POW cards come from Union entries found in the Thompson 4th Ark Cav, Co C CSA records.

Other dates on these "are also incompatible including the date transferred to Dept of West Ms for exchange=6/17/65; and then again as 3/4/65 transfer from New Orleans to Red River Landing exchanged. The 6/17/65 date is certainly suspicious since it is after the war was over.

I believe such discrepancies [including the name variances] are:
1-Not unusual in the world of Confederate compiled service records
2-Subject to the errors easily made by those soldiers recording such events
3-There is evidence that his original muster in date is carried forward to "some" of the subsequent units with which he served
4-Other muster in dates could conceivably be connected to one of his later units and not his original unit muster in date; especially if he is trying to hide any previous enrollments to avoid charges of desertion

These compiled service records [CSR] records can certainly be beneficial and often used by researchers. Still, care should be taken in determining what may be correct and what is not.