Remanufactured is really what it says. Pretty much a cracking tower process on a smaller scale that removes all impurities. Re refined would be the term. The base oil stock stays good and a new additive package is mixed in.
Years ago the Castrol GTX oil had a very distinctive odour. I got sent up to one of the if not first facilities at Fort McMurray for 2 weeks. They refined oil and used it in their equipement. Same distinctive odour. The used oils got recycled and run through the refining process again.