I don't think that we get serious image degradation with JPEG. You could try to take a TIFF image convert it to JPEG and subtract the JPEG image from the TIFF. What remain is a difference image, it will be mostly back.
The two major issues I see with JPEG are:
1) Information is thrown away. Highlight and shadow detail that may be useful may be lost.
2) Sharpening is normally applied to JPEG images. If you rescale and sharpen a JPEG image it may show haloes.
What I have seen in my experiment was that an mazing amount of info was retained in the JPEG image, but in many other cases perfectly recoverable tonality may be lost.
Eric I have been doing the same with my RX 100, but find that my JPEG files degrade after some editing in Lightroom. I have used JPEGS a few times to shoot with the camera HDR and love the results, but lose quality after Lightroom processing. I have been thinking of saving the JPEG to a
TIFF or DNG and working on that??