Old Spanish Colonial Sword-Curious Blade

[Jim McDougall]

This old Spanish sword I was told many years ago had come from the Carolinas. The striated shell guard vertical to the hilt, and the downward inner langet as with sash worn weapons. In posts about 2 years ago, it was suggested that the blade is notably newer than the hilt, but clearly a very old pairing.

The hilt form is suggestive of espada ancha in degree, but earlier in 18th century than the typical forms of the Mexican frontiers.
In the illustration from "Lore of Arms", William Reid, 1976, p.124, a Spanish sword by Corrientes (Toledo, Madrid, d.1733) is shown reflecting possible proto-form for the hilt from late 17th c.

The blade is backsword, 33.5 " long, and would seem a horsemans.
The puzzling thing is this elliptical central fuller, which does not seem 18th century, nor Spanish.

Can anyone help with identifying the blade, which seems pretty unusual.