Also, this is what my system displays:
Edit: it's reporting boxes after I change it to 0 to 40...
my guess is that there's some weird control character or something?
While dragging the input expression, hover over the left and right arrowheads following the variadic input slots. The white halo you see when hovering over an input slot will turn red and expand to include all the slots of that variadic input. Let go and it turns into INPUT LIST. This works for all variadic inputs, except for a couple of screwy exceptions.
I've actually found that the join block is really hard to get the red halo to appear sometimes. I find it easier if you get rid of all inputs, then drop the reporter on the arrowhead.
Edit: I might be wrong. If you are having trouble, then get rid of all inputs.