When I got my Day-Brite industrial, model IS232-UNV, it came with these two clear plastic pieces. I was confused about what these were for or where they even went. I eventually figured out that they are supposed to slip onto the edges of the reflector, but I am still not entirely sure what they do. The best theory I have come up with is that they are for tandem installations, where you would slide the pieces between the reflectors of adjacent fixtures to keep them more uniform. But what do you guys think? Is that the purpose of these parts, or are they for something else?

That's my guess as well, for keeping the reflectors aligned in tandem or row installations. I've seen them before in other brands as well.