I've never seen a Squareback '51 Navy Colt, whether it was an Original, Second or Third Generation, that has the loading lever screw enter from the left. Regarding the repros, who knows. And who cares, its a repro.
Crawdad, I don't want to argue semantics. Your Original/2nd/3rd gen "Colts" are your baseline, and it is obvious you disdain any "purely" Italian repros, and prefer anything that is branded "Colt" over anything else. That's OK. Your call. Your definition is correct. I do believe Colt used some Italian gunmakers in order to create some different "generation" pistols, though. Correct me if I am wrong.
For all of the rest of us that may be interested in repros (and I care), I have never been able to find any manufacturer or dealer that uses the term "1851 Navy Second Model" when dealing with Italian repro 1851 Navy .36 SB TG octagon barrel models.
Pietta brands this pistol as such:
http://www.pietta.us/products/Muzzleloadinguns/Navy/gallery/Navy_1851_18.html
In addition, Dixie Gun Works still sells the same pistol as the RH0850 Pietta M1851 NAVY YANK LONDON REVOLVER, which is quite a misnomer.
https://www.dixiegunworks.com/product_info.php?products_id=14047&osCsid=8t7brd43euh48c0u7ir1i1qve4
For all intents and purposes, with the rectangular cylinder stop slots and a rollmarked cylinder, SB TG, full octagon barrel, regardless of which side the load-lever pivot screw enters, that's about as close as one can get to a repro 1851 Navy Second Model these days. I don't have the money to entertain the "Colt" repros, and that is what they are: repros. You purists may defer.
I have a Pietta 1851 Navy Second Model SB but it was created from a RB TG model [2014 CM] with a SB TG from Pietta via Taylor's, so that doesn't count insofar as the screw being an original representation.
There is a gentleman on another forum who just received one last Tuesday from DGW, and he seems very pleased with it. Says he will post pics soon.
And these pistols all have the load-lever pivot screw entering from the left side.
Since you decide to ignore the repro Italians, that is your call.
And I thank you for maintaining a list of all folks belonging to the THR 1851-1860 Club. Kudos.
Jim