I apologize if I screwed up on this explanation, I'm getting somewhat punchy chasing this at such a late hour out here
on the Left Coast.

The recording of the incorrect unit ID for both E. R. Boon and Van Thomas is the result of the recording of the 1st Louisiana Cavalry Regiment from Federal POW records. Neither have file cards based on Confederate muster roll or other CSA type records.

It is a mystery why the Federal authorities listed their unit as the regiment rather than the battalion. Perhaps, they misunderstood the verbal statements of their prisoners.

These errors originate with the original Compiled Service Records which sometime in the mid 1900s were microfilmed. From these microfilm rolls, the Footnote/Fold3 records were developed.

What we find in the index of the breakdown of rolls for these two records at Fold3 is identical to the National Archives Microfilm rolls. See:

Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Louisiana. M320

Roll
1 1st Cavalry
A-Cl
2 Co-Ga
3 Ge-J
4 K-Me
5 Mi-Ra
6 Re-Ta
7 Te-Z
1st Battalion, Cavalry (State Guards)
8 2nd Cavalry
A-Br etc, etc.
Military Service Records, A Select Catalog of National Archives Microfilm Publications

The record of death for E.R. Boone, Card #6 of his record with the 1st Louisiana Cavalry Regiment, records him as 2nd Lt. Co. C/I? 1st Battn [Regt crossed through], Cav. All other cards in his file list his unit as the 1st Regiment La. Cav. At least we got one record correct!

There are no muster rolls found in the records of the 1st Louisiana Cavalry Battalion which could help explain the error was not found when the Compiled Service Records were originally developed.