Interesting Cristoph !
I don't think that they're the same courses, but I could of course be wrong. Flatirons was build around 1938, and while their website says that they were called Boulder Country Club for a time in the 1950's, if the date on your card is correct, the Flatirons course was not yet built at that time. The URL I listed above has a link to a scan of a scorecard from the 30's, and the hole lengths and distances don't seem to line up, although an analysis may find differently.
There IS a Boulder Country Club in existence now, who have a course designed by Press Maxwell, but they moved to their current location in the sixties. I'll see if I can find out any information on their previous course.