P.D.:
Apparently, I myself found an answer to the significant tonal differences in CMYK *.tiff exports using GIMP 3.0, which I mentioned earlier:
Before exporting, you need to embed the respective ICC color profile. Go to the Image menu, activate black point compensation, and in that same menu, within Color Management, within Soft-proof Profile, choose the desired color profile (previously installed).
When exporting (Shift + Ctrl + E), select TIFF extension, in new window select Export as CMYK and select Save Color Profile.
Now, you get consistent and coherent results for printing! Good percentage of similarity
BTW: Very possible than those differences of 93% or more, simply is because the ICC profiles are not embedded. I got much less percentage of differences
Apparently, I myself found an answer to the significant tonal differences in CMYK *.tiff exports using GIMP 3.0, which I mentioned earlier:
Before exporting, you need to embed the respective ICC color profile. Go to the Image menu, activate black point compensation, and in that same menu, within Color Management, within Soft-proof Profile, choose the desired color profile (previously installed).
When exporting (Shift + Ctrl + E), select TIFF extension, in new window select Export as CMYK and select Save Color Profile.
Now, you get consistent and coherent results for printing! Good percentage of similarity

BTW: Very possible than those differences of 93% or more, simply is because the ICC profiles are not embedded. I got much less percentage of differences