You have the situation where many of the men that were too old or otherwise exempted from formal military service served in Home Guards Companies and local militias and were from time to time called to active duty. These men very rarely appeared on records outside their own county records which have largely not been examined.
Then you have those men who became of military age after February 1864 went no records exist after that date. I believe that my Great grandfather was one of these men. He married in April 1865 at the age of 18 in what is now Grant County. His daddy was killed with the 3rd Arkansas Infantry CS at Chickamauga. You also have the example of Benjamin Riggs and his boys, whose exploits have been much written about, and David O Dodd.
On the Union side you have the group of men (possibly ex-Confederates) recruited/gathered by Gen'l Steele when he occupied Camden in April 1864. who were sent to Pine Bluff to be enlisted in the 4th Arkansas Infantry US with the wagon train that was attacked at the battle of Mark's Mill. These men where supposedly executed for treason along with a company of unarmed african decent soldiers who had accompanied that train as Pioneers. I beleive that there were also teamster and other blacks in Uniform who shared the same fate because they also wore the union uniform or were recruited to be enlisted at Pine Bluff in one of the African Decent regiments.
Then you have the case of those men who "fell throught the cracks" like Benton Musgrove. Who joined the 19th Arkansas Inf. CS and came to Pine Bluff but died in hospital before there was a formal muster roll made of his enlistment in August of 1862. Bentons record, what little there was of them, became lost when Hardy's Regiment (sometimes referred to as the 19th/24th Arkansas consolidated Trans-Miss) was assigned to Frost's Missouri brigade during the battle of Little Rock and found their way into the Missouri state archives where the only record of him is that he was listed as being one of Missouri war dead. There are plenty of indication of several such records being lost in this manner at the camp White Sulphur Spring Hosiptal and I am sure that this occurred at the Little Rock and other hospitals also.
Then you have people like Byran Howerton whose excellent research has given us men from Arkansas who enlisted in Louisiana, Missouri, Tennessee, Texas and Mississippi units. And likewise those from these same sates who enlisted in Arkansas regiments.
In my estimation almost every ablebodied white male in Arkansas in the 1860 US Census and those who came of age during that time would have served in some manner. Add to that those who who were less than ablebodied who served in lessor roles as home guards and governmental authorities such as sheriff. Then add to that the numbers of blacks who worked on building entreachments around Little Rock for example, or Arkansas Post, or Fort Pleasent or doing other logistical work for both side.
There are just some of the exemptions that I have run across in my limited focus of research and I am sure that other researchers have run into the same things, if they have looked deeply enough. When we define what constitutes service too narrowly to just those whose names appear on the "official muster rolls" what servcie or disservice do we do to the preservation of history? Therefore, I tend to go with the higher numbers for the Confederates at least.
We have no problem with counting all the Arkansas US regiments as being totally made up of Arkansas men. But, many of the Union Arkansas US Regiments contained many men enlisted in Kansas for example. So were they "true" Arkansas enlistment?
That is the one thing that troubles me with the Sesquicentennial of the War over the next four years, especially in Pine Bluff, that even with all the "New" information discovered, and the studies done, the powers that be seem to be only interested in telling the same old tired story.