If part of your intent is to teach students to use the tools in Desmos calculator, ignore this, but if you’re having students select the regression on Screen 15 so they can compare their estimates to the actual regression, you may want to make use of @Steve_Rinard ‘s suggestions along with using a hidden folder in the graph, so you can pre-define any values you want to pull, like below:
The reason you have those green error icons is that referencing values from a full screen graph is unreliable. If students don’t use the variables you want or they create a second instance of the same variable name, the CL can’t pull them. (I’m using a numberList instead of separate variables to just pull the list once, values = this.numberList(`V_{alues}`), and index after, a = values[1], b = values[2], etc.
If you’re looking to give students the correct values, you can name them in a way students are unlikely to create, so that your CL will more reliably pull the values you intend. You’ll still have the green errors, but they’re less likely to be relevant.
I didn’t thoroughly look at your activity, so this may not be helpful. You may at least know the reason for the errors though.