Tom, Thank you for such a thoughtful and thought provoking answer.

I think your surmise about Zachariah is an excellent one that does throw a plausible monkey wrench in the "Jenks-Walker mix-up" theory.

Here he is from the 14th Iowa Company E roster:
Walker, Zachariah. Age 22. Residence Vandalia, nativity Indiana. Enlisted Sept. 28, 1861. Mustered Nov. 1, 1861. Discharged for disability April 2, 1862, Pittsburg Landing, Tenn.

If he was called "Zach" by his companions it would be very very easy to get his name confused as short for "Isaac". I will try to locate him after the war to see if we can rule him in or out but I didn't find him in his supposed hometown before the war yet. I will keep looking. And I am not sure if he applied for a pension which might rule him out. His service file might reveal something. As a park employee do you have easier access to the NARA files?

Some hitches I see in the "Zach is Isaac" theory: if he was discharged before the battle and died some unspecified unknown time later, even if in the Pittsburgh Landing camp, would a discharged soldier still have made it into the ROH? And would a discharged soldier, even if ill, have been allowed to remain in an army camp or would he have been boated out on a hospital steamer as quickly as possible?
If he died of disease in camp his identity and his death would have been more likely to be well recorded, and his body would not have been disfigured, a serious problem for a man like Jenks who may have laid in the sun a day or two before burial making his indentity less certain. Jenks would have more likely been in an unidentitfiable grave than Zach perhaps, so the odds favor the "Isaac is Jenks" theory I think better. Then again, even well marked originally, a Zach marker might have been lost as easily as any other during any reburial. It complicates the puzzle doesn't it?

I didn't mean to imply that Jenks was the only death in the Company whose burial was unknown, or the only one who wasn't in the ROH, but that he was the one man I had asking about in an earlier post. Your more complete list of casualties is of course correct. My point was that if Isaac Walker of G was not dead, and we can say for sure he was not, it might be most likely that it was his "lost" hometown friend who might have been the one most likely to have been misidentified as Walker if the two had been closely enough associated to be confused with each other.

I am betting Isaac Walker of Nevada Iowa had no idea when he was farming for thirty years after the war that his name was listed among the dead.

Two of the men you named above as buried at Shiloh but not dying at Shiloh are interesting cases. I don't know about the others but will look into them more sometime. Here are the two that I find notable:

From 14th Iowa Infantry Company K:
Rolan, William C. Residence Lawrenceburg, Tenn., nativity Tennessee. Enlisted March 28, 1862. Mustered March 28, 1862. Killed in action April 6, 1862, Shiloh, Tenn.

This local man lived close to the battlefield and enlisted just days before the battle as Grant's troops assembled at Pittsburg Landing. He stepped forward and volunteered. One account says he was among those captured with the regiment at the Hornets' Nest and marched off to Corinth. While waiting for a car to rail the prisoners away from any rescue attempts, they were held under guard at the Corinth railyard. It is said he was recognized by neighbors or a brother-in-law from Lawrenceburg, pulled out from among the Union captives and summarily executed in cold blood as a "traitor". Hung or shot I don't remember but he certainly paid the full price for his loyalty to the Union cause. Two Lawrenceburg friends who had enlisted with him were not recognized and remained hidden among the prisoners. His story is memorable and deserves to be on a statue, or plaque at least, in Corinth, as a brave patriot who faced more danger, ran more risk, for the Union than the Northern men of his regiment. He was no spy but he gave his life for our country as surely as Nathan Hale did. But he is all but forgotten and the roster says KIA. I wonder where he is buried?

The other remarkable man:

From the roster of the 14th infantry Company G:
Cheney, Alexander. Age 25. Residence Davenport, nativity Germany. Enlisted Nov. 1, 1861. Mustered Nov. 4, 1861. Wounded April 6, 1862, Shiloh. Tenn. Died of wounds July 10, 1862. Buried in Shiloh National Cemetery, Pittsburg Landing, Tenn. Section C, grave 7.

Cheney's story is also memorable. He was shot over the eye I believe, the bullet entering his brain. His fellows checked his body, found no sign of life, even stood over him for some time firing at the enemy before moving on. The regiment was captured. Grant won the following day. Burial parties went out the next day and when they moved him for burial the party discovered he was alive. He was hospitalized with this terrible but amazing wound, and even recovered enough to speak and describe his ordeal, even giving the names of the friends who had leaned over him and fired over him etc. He had been fully aware but completely unable to speak or move when they had hovered over him in the thick of the battle and during the time he lay waiting for help to arrive. I do not know how long he was conscious and communicative afterward in the hospital. Of course the wound eventually became infected and he died but if the roster information is correct he had lingered for several months with this hole in his head. His medical file might be a very interesting thing to read. His story is briefly mentioned in a Time-Life book.

Tom thank you for your input on this mystery. From looking at the photos and information on Walker on the cemetery website I did realize when I posted that it was an Unknown grave for Walker but his name is still on the official burial list, and in the ROH. I thought we might be able to better identify the man who is buried there even if the grave itself is not known.

Even if his exact location is officially unknown, since Isaac surely is not buried there, my hope was that Jenks might be at least added to the probable list of Unknown burials in place of Isaac's name, which we can easily prove is an error. Your Zach theory complicates matters considerably though as another plausible alternative, and perhaps it is just too late to say anything other than it is not Isaac Walker in that grave. Maybe Zach will be found with alive afterwards with more research and maybe he can be ruled out. Maybe Jenks will turn up buried elsewhere too.

Maybe someone else here is information on any of these men, it would be great to have more information on all of them.

Thanks Tom, I would love to meet you sometime. PS You are close by Lawrenceburg, perhaps you can find more concrete information on Rolan.