Some day it would be special to visit the battlefield on the anniversary, and maybe even to do the hike up from Corinth as part of the deal. Our lad's unit was cheek and jowel with Johnston when he toasted Statham's Brigade just before his boot filled up with blood. Like I said it was the Battle of the Somme for Iowa due to the massive losses. The governors of IA and ILL rushed leased hospital boats, medical staff and supplies to Pittsburg Landing and our state gained a substantial rear-echelon federal hospital at Keokuk (which then produced the state's only national cemetery, now we have two). Keokuk was just below the winter ice limit and was deemed to be just above the threat of miasmic vapors and southern diseases.
The high number of escapees is impressive indeed and in my opinion might be one of the salient themes in your work. Who would have guessed that the camp was that permeable!
As for other sources, looking at any post-Donelson muster rolls might be useful even if they were abstracted. Probably useless cause of what you already found with the 54th--the noise from Shiloh losses would override anything earlier. One wonders how many escapees might have simply slithered home glad to be able to do so. There were the petitions for pardon and taking the oath by several of the captured regiments which brings this to mine. Suppose those have signatures from the prisoners? You could look at Camp Chase records that were not carded. Lindsley's Annals have some casualties but you no doubt have been there.
A fun thing that bubbled up here just today is a Davenport 1863 city directory listing in which a fellow lists "Confederate Army of the Potomac" after his name and before his address--can't figure what he thought he was doing!