I can't think of why it would make any difference to the reliability of the cottered joint. But, most (not all!) of my many Raleigh Sports have the cotters factory-set the same way; i.e. the nut is up when the crankarm is forward. I replace them the other direction because I think the rounded cotter end is less prone to catch cuffs when riding in long pants.
I doubt that factor was of much concern to the builders of the beautiful Paramount.
David Bean
Arlington, MA
beandk at are-see-enn dot com