The recipe writers of this world are not trying to help you save space in your kitchen by specifying evaporated milk and then expecting you to reconstitute it. They want the richness and smoothness of full-strength evaporated milk. If they wanted reconstituted evaporated milk, they would just tell you to add milk.

(If you run across a recipe from someone who wants you to reconstitute evaporated milk, find another recipe - the recipe writer is a quack….)