Tom things are even more confused than ever it seems.
There seems to be only ONE Isaac Walker, not the TWO as we have been talking about earlier.

We were originally trying to identify an Isaac Walker of Company E 14th Iowa Infantry who is listed in the ROH. We found two other Isaac Walkers, one in Company B and one in Company G, listed in the Iowa Roster and Record, but none in Company E.

Now it seems that the Isaac Walker of Company B, 14th Iowa Infantry, whose name is listed in the Iowa Roster and Record as you found, may not ever have even existed. The Iowa Roster and Record may also be in error because this Company B Isaac Walker is NOT found in the NPS Soldier Sailor System website.

An employee at NARA told me the Soldier Sailor System drew up their list of names from the Compiled Military Service Records found at NARA. If that is true, then NARA probably does not have any military service records for any Isaac Walker of Company B, who supposedly served in the Dakotas according to the IRR.

Looking at the 14th Iowa soldiers listed on the SSS, there is only ONE Isaac Walker found in the entire 14th Iowa and he is the one from Company G. So NARA probably has records on only this Isaac Walker.

So if the ROH lists a real soldier from the 14th Iowa named Isaac Walker that name applies to only one man, the guy from Company G, and there is no doubt he was real and that he went home before Shiloh and lived long after the War.

That does leave your Zach Walker of Company E as still the best bet for the real guy in the ROH but we don't know if he died or not.

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But now to complicate things further, in Company E the SSS does list an Isaac WALTER or WALTERS (they show both spellings) of Company E and he is also in the Iowa R&R. That name is very very close to the ROH Isaac walker of Company E.

I thought WALTERS might be the true soldier named in the ROH and who might now be buried at Shiloh but when I found him in the IRR, this soldier did not die either and he didn't enlist until long after Shiloh.

Here is his roster info:

14th Iowa Company E:
Walters, Isaac. Age 21. Residence Jasper County, nativity Pennsylvania. Enlisted July 24, 1863. Mustered July 24, 1863. See Company A, Residuary Battalion Fourteenth Infantry

14th Iowa Residuary Battalion Company A:
Walters, Isaac. Age 21. Residence Jasper County, nativity Pennsylvania. Enlisted Jan. 22, 1863. Mustered Jan. 22, 1863. Mustered out Aug. 8, 1865, Davenport, Iowa. See Company E, Fourteenth Infantry.

Bottom line: the Iowa R&R doesn't agree with the SSS and NARA, and with the ROH, they all disagree it seems. There probably will never be a way to sort it all out.