In a way you have described the life cycle of any of the few Provisional Enrolled Missouri Militia (PEMM) regiments. They were created from selected units and men of the troubled EMM apparatus in spring of 1863 (this equates to your 23 May 1863 date). The PEMM regiments were intended to be "super EMM" units culled and detailed from the best of the 9-month-old EMM outfits. The PEMM were casualties of the growing fight in Missouri State politics between the "radical" northerners who wanted to stop the rebellion at any cost and the "moderate" northerners who were hoping to convince their wayward southern brethren to come back into the fold peacefully. The moderates were in the majority of power positions during 1863, so they shut down the PEMM (which, by their nature veteran combat troops were usually "radicals") in the fall of 1863 (this equates to your date of 22 October 1863 date). In truth, some PEMM regiments--particularly those in SW MO-- performed well and were kept around until a better system could be devised in 1864 to plug them into new units. The same PEMM men simply kept on performing either as PEMM or in their original status as EMM until they could be converted into a new system in summer 1864--either new Missouri Volunteer Cavalry Regiments or the part timers of the General Orders #107 home guard-like armed self defense posses. What I want to emphasize with a large number of the PEMM men is that they were by this time in the war determined anti-secessionists dedicated to stamp out the rebellion any way they could. Lots of these guys were "shoot first and ask questions later" kind of militiamen.
Elements of the 68th EMM Regiment were detailed into Companies K, L, and M of the 8th PEMM in SE MO.
I was not aware this unit was mostly corporals and sergeants, and I cannot account for that phenomenon.
Does that help?
Bruce Nichols