Is it possible your images are 5x7 prior to cropping? What is the original image file dimension?
Are you actually cropping something away? Or are you just trying to resize the images? LR doesn't do any resizing at all until you export or print the image.
Thanks for the input Mike. It seems the images in question were possibly cropped earlier to 5x7... these show "As Shot". But what is odd is that if I crop them down further (with the 5x7 aspect ratio locked) they don't show "5x7" but continue to show "As shot" when I return to them, despite the new 5x7 crop border. Weird.
Lightroom never makes changes to original files, including crop, it just stores the info in the catalog file to provide you with the correct display 5x7 aspect ration. You need to export a copy of the file and resize appropriately.