Godot is strictly object oriented. When you define a var it becomes part of the object that the script is attached to. So when you access
pts_rest from within the first script you are looking for the
pts_rest-value in the first RichTextLabel and when you are doing it from within the second one you won't find it since that one doesn't have a var called
You need to get a reference to the first RichTextLabel in order to access the variable. The easiest way to do so is to use
get_node(). In your case that's ok, since all nodes are part of the same scene.
By the way I would recommend moving the code into a script that is attached to the base node of the scene (the one called "TextureFrame"). After all you are programming a new complex control, not a collection of smart buttons. It's not really the RichTextBox's job to know how many points are left, that's something the whole control should take care of.