Jefferson Davis if he hasn't already been mentioned
That's a really interesting choice!
Quick Warning: don't read the rest of this unless you're interested in nerdy analysis of a reconstruction era SCOTUS case.
Respectfully, wouldn't the SCOTUS ruling in Texas v. White preclude him from being considered POTUS? There were a bunch of issues in that case that mostly dealt with what was going to happen with Texas during the reconstruction era. In addressing one of the many peripheral issues, though, Justice Chase opined that Texas had never been outside the Union and any action taken taken by Texas to declare secession were basically, for lack of a better word, voided (paraphrasing). In other words, my understanding of the decision on this particular issue in Texas v. White is that, in the eyes of the United States government, Texas, and by the extension of the precedent set by the decision in this case any other state that seceded to make up the CSA, were never part of a sovereign nation, but were rather still a part of the union and under the control of an insurrection for a couple of years.
Now, just to reiterate, the main issue of that case wasn't whether or not Davis would be considered a President, but I think it can be argued that one of the far reaching implications of the decision is that he wouldn't be considered a former POTUS, or perhaps even that he wouldn't even be considered a President of any nation at all.
That being said, I'm from Massachusetts, so I've never really been exposed to the southern perspective on these matters. I've heard that the southern perspective on this era in our history is a very important part of the southern culture - I really hope nobody takes this comment the wrong way - not looking to insult anyone haha!
Also - full disclosure - I never read the dissent in this case (or really any dissents in any cases in law school) so I have no idea what it says (haha).
Slow day on my end.