Previously, I had no problem taping outside corners with waterproof adhesive and joint tape, but now there are a few extra millimeters of gap that needed to be filled, which means the joint tape doesn't have much adhesion on one of the boards.
I thought I could start by gluing the 50mm strip shown in the second picture, then come back a day later to glue the joint tape to the outside corner. I can't see any problems with this, but I wanted to double-check before I start.
I have all the materials at home, so I'd prefer to avoid having to go out and buy any corner profiles.
All help is graciously accepted!