You can try renaming the original files on your back up and convert them to dng as well and connect them to the missing images by following the below article.
Adoeb DNG converter :
There is no Lightroom function that will match renamed photos to un-renamed photos. You will have to rename or relink the photos one by one if you want to be able to use them in Lightroom.
What's your renaming scheme? Would you be able to import copies of backed-up originals into a new temporary catalogue, rename them there, and then put the files in the folders where your catalogue expects them.
If the missing DNGs are still shown in your Lightroom catalogue, you could try using my Syncomatic plugin . You would import copies of the backed-up originals into your catalogue, select them and the missing files, and use plugin's capture time matching option to match originally-named files with the corresponding renamed thumbails. Test on a few pictures first.
thank you for your help, i think this is the only way to solve my editing. i have to rename the original dng files in the finder folder. (i have convert them into dng-files when i have made the import to lightroom so i have already dng files in my backup.) as i have deleted some of the pictures during my editing i have to check every picture in the finder with the ones in the smartview of the lightroom catalog and rename them according to it.
thank you for your anser, i have to try it this evening. i have around 700 pictures and of them i have deleted 100. i have only renamed and exported 600 of them. so i have to check every picture and rename it.
but i'm happy that i have still my backup.... ;-)
Thanks a lot for your support. i renamed it as "user defined". i think your suggestion would be perfect if i have not denied files in lightroom during editing the photos. after my editing i have selected only around 600 pictures (from 700) and renamed them. so there are still 100 pictures in the backup folder which i don't need. so i think i need to act like sarika and dj told me.
but i like a lot your way and i really appreciate your help
thanks so much to you all of you for helping me so quickly