Your math is correct about the 90-day service expiration for the Sumter Regiment, Louisiana State militia. Officers and men should have served until the end of May 1862, or perhaps a day or two longer.

The point is that most did not.

Since Confederate law took precendence over state laws, members of militia units were not exempt from the Conscript Act of Apr 16, 1862. As mentioned in my previous post, the Conscript Act required that all white male citizens subject to military service (age 18 - 35) were required to be enrolled in Confederate military service within thirty days. The deadline was May 15, 1862.

Whether or not a man belonged to a militia unit made no difference. Of course, if a man happened to claim citizenship in another country, he was exempt from the law.

Members of the Sumter Regiment who were eligible for military service were discharged by virtue of enrolling in Confederate service. The new regiment organized on May 15, 1862, within the thirty-day limit. A few remaining members of the regiment not eligible for conscription may have served out their 90-day terms.

The same kind of event took place all across the Confederacy, leaving many men across the South angry and confused. Most complied by enrolling in Confederate service as required by law.