there are photos I've taken that are publically available, but aren't in my photostream, because apparently my photostream is not collection of all photos I have on flickr. I think it's because the Lightroom plugin interacts with the photostream as if it's any other album, so if you happen to have uploaded a photo to flickr through a means other than Lightroom, or upload it via Lightroom but then remove it from Lightroom or delete your catalog accidentally, Lightroom just magically deletes those photos from your photostream--they're still on flickr, but the only way find them is if you already know the link from somewhere else, or if you find them from the albums page on flickr, which will show you photos by a user that are not in that user's photostream, the page that shows you all of a user's photos. If the photo is not in an album, and you have lost the link to it, that picture no longer exists, or at least cannot be found, unless you can guess the number assigned to it.