I never realized this bit of history about Ricardo Montalblan. I always thought that the clip in "A Matter of Honor" was filmed live and made to look as if it were years ago, similar to Anne Baxter in "Requiem For a Falling Star" dressed up as a man.
Interesting. I wonder the same thing every time I see it ... no doubt a young Montalban from some obscure film early in his career, but definitely Montalban, not his sister, and not as far back as 1940.
The clip in "A Matter of Honor" showing Ricardo Montalban as a young matador is from the film "Santa" (1943). There's a video on YouTube that shows highlights from it: