Thank you for this. If I understand correctly, I can upgrade 9.0.43.6 with 9.1 by running the service pack. Then after the Service Pack, I will be able to install the Cumulative Updates on top of 9.1. Am I right?
EDIT: Attempting to update DB will fail. So I'd say that trying to upgrade from 9.0.43.6 to 9.1 is not going to work.
By the way Dynamics 365 9.x is probably the buggiest and messiest version of Dynamics I ever came across.