Hello again Matt,
I have been working more on this and going through files and more books.
In reviewing the book "Spanish Military Weapons in Colonial America 1700-1821" I looked at the military blades much like yours. While these are typically noted as 'Spanish military blades' I notice that they most often have triple fullers in the upper third of the blade, as well as flattened hexagonal cross section. In checking "Armamento Portatil Espanol 1764-1939" (B. Barcelo Rubi, Madrid, 1976, p.26) I notice that the Spanish military blades of regulation pattern, in this case M1768, which are supposed to be the type used in the New Spain swords, do not have the triple fullers.
This would suggest of course, that your blade was not made in Spain.
In studying these Spanish colonial weapons of the latter 18th thru early 19th century, there has been some suggestion that many of the 'Spanish' blades found on the early espada anchas as well as the sabres carried by militia officers may have been Solingen made. It is interesting that the triple fullers also appear on early trade broadsword blades from Germany and are often found on kaskaras and Omani kattaras.
On the hexagonal cross section 'Spanish' blades, it is most common to find the inscription "No Me Saques sin Razon" on one side and on the other "No me Embaines sin honor'. It seems that virtually all of these blades carry this inscription, though there are variations.
In reviewing coin books and material on the Mexican eagle symbol, I can find absolutely no evidence of an eagle in the posture seen on your blade, with fully outstretched wings. It was very good research on your part to find the Disturnell map showing a comparitive example to the engraving on your blade.
Apparantly there is a great deal of complexity in the content of that map, which was placed with the Treaty of Guadelupe-Hidalgo in 1848, at the end of the Mexican-American War of 1846-48. Interestingly, John Disturnell of New York copied the map from the so called Rosa map (Paris, 1837) who in turn had copied it from Henry S. Tanner map (Philadephia,1826).
It would seem with all of this, that the eagle style shown on the map may very much reflect American style.
Earlier it seems you mentioned PDL , which is actually P.D.Luneschloss, a Solingen maker who supplied blades at about the time of the civil war, and before.
With a great deal of speculation, I would suggest that possibly the German maker, exporting blades sometime c.1850's may have decorated the blade for a Mexican officer on special order, most likely in some diplomatic venture. It seems plausible that he might have been aware of or used the eagle on the Paris map as a model for a Mexican eagle?
Since it is well known that the Confederacy had considerable contact with Mexico, it would seem quite plausible that the blade, or entire sword, may have come into thier possession. As I have previously described, Custer captured a sword from a Confederate officer during the Civil War which was mounted with a blade carrying the familiar 'Spanish motto' that I have indicated often found on the triple fuller blades.
If the blade does have the PDL, then this scenario may be the answer, and would pretty much eliminate Oaxaca.
I very much enjoy this kind of research, and really appreciate your reciprocation and response in exchanging ideas!!
Please post some photos of the entire sword, and confirm the PDL marking OK.
All the best
Jim