By the time Jackman's Missouri Cavalry Regiment (1863-1864) was formally organized as a regiment, communications between the Trans-Mississippi Department and the Adjutant & Inspector-General's Department in Richmond had all but been completely destroyed. Nobody was going to risk an officer's capture just to take a bunch of muster-rolls to Richmond in 1864, with having to cross both the river and some 100 miles of Federal-controlled territory. Hence, Jackman's regiment never got an official designation beyond "Jackman's Regiment of Missouri Volunteer Cavalry".

The 16th Infantry was about the last of the Trans-Mississippi units to receive a formal designation from Richmond, and it came out in late 1863 (except for a bunch of Louisiana units, whose existence was apparently reported by Lieut. Gen. Richard Taylor in 1864, when he was appointed to command the Army of Alabama, Mississippi, and East Louisiana, and he wanted to get his old First Army Corps from the Army of the Trans-Mississippi transfered from that old army to his new one). Frankly, the 16th was lucky to get one, and the fact that no 13th, 14th, or 15th Infantry unit can be identified shows how little Richmond was aware of circumstances in the West. I suspect that the War Department had issued permissions to various officers to raise those non-existant units and designated the 16th at that number owing to their uncertainty as to the existance of those three units. So, Jackman's cavalry was really too late to get a formal designation.

For that matter, Headquarters of the Army of the Trans-Mississippi all but formally denied the existence of the regiment. If you've seen the quarterly returns for the Trans-Mississippi for September and December of 1864 (the only ones that are even marginally complete), you'll find whole divisions missing--see if you can find Shelby's division in either of the reports (one might be able to forgive the September one, but by the end of December a staff officer preparing the quarterly report couldn't have been unaware of the division--it was camped only a few miles from Shreveport!). Gen. Edmund Kirby Smith was flat-out lying to Richmond about his strength to keep it from being ordered east of the river. So, Jackman's whole brigade doesn't appear, let alone his regiment. Nor do about 30 other regimental-sized units. The bulk of these units are cavalry, but whole brigades of infantry and battalions of artillery are missing from the quarterly returns as well. Curiously, they do show up in after-action reports, including reports for the Camden and Red River Campaigns as well as the Missouri Campaign of 1864.

This is yet another reason why trying to trace Missouri Confederate units is a real trial. I've devoted some 20+ years to it and can state that I'm just beginning to understand how little I understand about them!