Thanks for this info, Steve.
One article Steve posted a link to, showed the results of an experiment, using a 19th C, Japanese wood block print, exposed to daylight, over a period of 6 months; it was divided into thirds, with 1/3 behind UV film, 1/3 unprotected and the 1/3 control section covered with foil. The experiment was extreme, as no one would (hopefully) place a print or poster on a wall that receives direct sunlight; the results were still astounding, especially in the assumed belief (by many) that UV plexiglass provides protection against all types of light. The UV-covered section appeared (to the naked eye) just as faded as the unprotected area. The test also used a modern reprint, which showed little effect from the sun's rays during the same length of time.
Translating this to film posters, it would suggest that older posters are more susceptible to noticeable fading, versus newer posters that have been printed on glossy paper with modern inks. But all works on paper are at risk from light, UV or otherwise.
(http://www.ukiyoe-gallery.com/ukiyoe/sunfade6.jpg)
(http://www.ukiyoe-gallery.com/ukiyoe/sunfade5.jpg)