My beat is guerrilla warfare, so my comments relate only to how these sources match corroborating sources in that subject. Also, the sources you name mostly deal with the west-central Missouri guerrillas (and a little to northwest MO north of the Missouri River), so I gather that you wish me to restrict my remarks to that area.
I agree with your postive assessment of the St. Joseph and Liberty weekly newspapers. The Kansas City "Journal" leaves me flat sometimes, since it concentrates on business and especially that of the Santa Fe Trail and the plains. Some of its news articles about bushwhackers even nearby are only two to four lines. Their coverage of guerrillas attacking river shipping seem geared to the business investor whose stock is at risk. The "Lexington Weekly Union" has some good coverage of guerrilla warfare. All of these papers have a northern bias, since they would not be allowed to print without one.
Regarding guerrilla memoirs and their "accuracy in detail and fact," they vary from event to event that they describe. What they omit is interesting, but you have to remember that these men wrote at a time when they knew their grandchildren would be reading what they printed. Further, there was much more respect for "the Lost Cause" in the early 20th century and more acceptance of their views. They were all quick to justify what others dismiss as outlaw behavior, and I agree that they needed to do that to counter the northern bias in what was already in print. On most of what they wrote I have seen McCorkle's, Walker's, and even Cole Younger's reports verified by other sources. Even Jim Cummins' material is accurate on some things. Further, each of these offers some unique events or viewpoints on certain events not experienced by others. Far worse is Harrison Trow's material in his 1923 book written by Burch. It struck me as funny that it almost seems as if Trow was rather faithful to the facts in entire chapters while other chapters were so full of fancy. This mostly applies to events in which he participated versus what other guerrillas told him, but not always. I have found Bill Gregg to be accurate on a higher percentage of what he wrote than most of the others. Maybe his years in law enforcement postwar gave him a greater appreciation of accurate reporting. Many of the other guerrilla accounts that Donald Hale dug out of postwar newspapers are rather factual, although some of them stuck to general topics.
I am nearly alone on my assessment of John N. Edwards' "Noted Guerrillas." Yes, his prose style is drippy, you can throw out his casualty figures (if you add up all the dead Yankees there weren't any left west of the Mississippi River), and he mixed up events terribly. However, I have found SOME of the events he narrated and the lists of guerrilas who participated to be surprisingly factual. The really hard part working with Edwards' stuff is that you have to collect so many corroborating accounts to be able to sort out the junk from the facts. (That's also how to pick out the frauds, like Dalton's, too.) There is much truth in these memoirs, but digging it out is so difficult. A lot of the Union commanders Edwards names were not involved in the events as he describes them. Yet, many of the events Edwards covered are only corroborated by obscure newspaper articles and other sources hard for readers to find.
In fact, all the guerrilla memoir accounts mixed up specific events, and Edwards did because his sources were the bushwhackers themselves. Much of the reason for this is that these men fought in very similar fights over three separate fighting seasons. It was easy to jumble them up in their memories, especially if comrades weren't present to help straighten them out.
Does that help?