So if your car takes 4.2 quarts of oil and you needed to add 5 extra quarts over the course of a 20,000 mile OCI, why not just do a 10,000 mile OCI in the future?
Everything looks ok the only concern I have for your 20K OCI's is a bit of oxidation. If your going to use a non extended drain recommended oil I would cut the OCI to 18K miles.
I'd like to do a 50k oci but I just can't do it without a higher stock oil capacity. If I have a 5qt pan and a oil cooler I still wouldn't go past 20k. Did around 12k with tbn left but I wouldn't feel good about it