So the situation you’re describing here is unfortunately a flaw in our system that we’re currently working on. Due to the way some projects are set up we need to make it so that they Create a project so their demo levels run smoothly. What you’re seeing in the Vault is a cosmetic issue. No matter what type of project it is, the Vault will always say “Add to project” but function the way it’s intended when you select it. That’s why Water Planes lets you add it to an existing project but SuperGrids needs to create a new one.
For now the migration steps above should allow you to get the assets you need and we are working on a solution for this in the meantime so don’t worry! Here are the migration steps again for you:
Step 1: Create the project you wish to work on.
Step 2: Open the project file you wish to migrate (ex. SuperGrids)
Step 3: Right click on the asset you wish to migrate and select “Migrate”
Step 4: Select Okay and the Project you wish to migrate the files to.
I hope that answers all of your questions and let us know if you need any more clarification on anything.