I deleted images on the hard drive by mistake, does that delete the catalogue data as well? I'm not sure if it does because when reimporting those same images from a backup the image names are changed to xxx.DNG-2 and not xxx.DNG as they were originally. Why is that? How do I find the catalogue data for the original images and apply that to the re-imported ones...? Or does such a thing exist, or do I have to redo the PP all over again...?
if you delete image on the file system LR does not loose any development settings (sometimes it can not display a preview, but this does not mean that the development settings are lost). LR shows a "!" for lost images.
You need not to reimport the missing image! Just copy to image from your backup to the location where LR expects the image and keep the same name as in LR for your image. Then, the "!" disapears (red mark) and (nearly) everything is o.k.
For some of your images the develoment data stored in the catalog is more recent then the information stored in the (jpeg/tiff/dng) files. You should select these files and choose "Metadata->Save Metadata to File" from the context menu do sync lightrooms catalog with the files on the hdd. (green box)
Thanks for the answer, it confirms what I was expecting.