The article says that the depiction of the Apostle Saint James in the stained glass window is inspired by the statue at the main altar (cape, staff, gourd, cross) and the miniature in the Codex Calixtinus (benediction gesture). The decorative elements are neo-Romanesque. I guess that one could say that it is an amalgam of Saint James the apostle, Saint James the pilgrim and Saint James the Christian warrior knight.
Thank you all so much! I would like to say that it amazes me how much knowledge there is and how helpful people are on this forum, but it doesn't amaze me any more. I am just amazingly grateful.
And, just think, if I had asked this question two years ago, the article in Galicia Histórica would not have been available!
The window was made by Joan Espinagosa (1858-1931) "Little is known about his career, although he appears to have travelled around Europe, imported a machine from Germany in 1903 to unpolish glass and brought printed glass to Spain for the first time from Britain. He is known to have won a gold medal for a stained glass window [not the one over the Holy Door] at an Exhibition held in Santiago de Compostela." [artnouveau.eu/en/author.php?author=195] [The Exhibition was in 1909.]