At their period of time when large families were prevelant, many men were named after famous individuals. In my case, both my
great grandfather and his father were named James Madison Martin. My grandfather, George Washington Martin.

"It is not clear if the muster roll was taken after the first day or before. In other words, were they taking a head count after the first day's battle or prior thereto?"

No -

A. J. Martin of Co. G, was recorded on the two subsequent bi-monthly muster rolls. Musters were required to be conducted on the last day of even months if at all possible.

In our case here, he is noted as missing from April 7, 1862 following their involvement in the Battle of Shiloh. These musters would have been held April 30 and June 30th, respectively, at the earliest.

Company G

March & April, 1862 muster roll, recorded Absent Missing from Shiloh April 7, 62

May & June, 1862 muster roll, recorded Absent Missing at Shiloh Apr 7, 62,

Appears on a Register [not dated] containing a report of the Killed, Wounded and Missing of the Second Corps, Army of the Miss., at the Battle of Shiloh, April 6 and 7, 1862
Time and place of wound Apl 7
Nature of wound ___________
Remarks Missing

Note: This register would have been compiled sometime much later, most likely by the Corps. Commander, compiled from unit commanders after action reports.