The copied instructions are for the from scratch variation. The OG with premade mayo has you huck everything in there, and that’s what I typically do. I usually mix the mayo and water before I add the rest of the ingredients so I can get the consistency right, but I don’t think it would hurt anything to wait to the end. We mix it with an electric whisk just because it makes for slightly easier dishes.
I can’t speak to any of this, I’ve never attempted the from scratch version. I copied the recipe and instructions just to preserve them.