Lightroom :: Using DNG Files For Backup?

Is my image backup plan fundamentally flawed? My lightroom catalogue refers almost exclusively to RAW files, but for each file, once I've done the required edits, I "export as DNG" to make a backup which has the edits embeded in. I prefer to use RAW files as the main file but I save the backup as DNG just to save a bit of space)
 
However, if I replace a folder of RAW files myphoto1.CR2, myphoto2.CR2 with a folder of DNG the equivalents myphoto1.dng, myphoto2.dng then not surprisingly Lightroom shows the files are missing. (At this point all I'm doing is simulating a backup recovery).  I can "find missing folder" easily enough and the ? disappears from the folder list, but the individual images in the library are still missing. Again this is not really surprising because although the file names are the same as those referenced in the library the extension is DNG rather than RAW.
 
Now the surprising part (for me anyway).....I can "find missing file" by pointing to the replacement DNG and it warns me that the file name is not the same (because the extension is different) and asks if I want to link them anyway. I say yes and once again the image file is linked to the image reference in the library. So far so good, BUT, despite ticking the box which is meant to link neighbouring files, only the one image is linked.
 
Clearly if I do face disaster and need to use my backup DNGs then I can't go individually linking each and every image. Is there a quicker way, or is my backup plan fundamentally flawed?