When I got 525, the guard was rubbing at 1500 miles. We purchased 3 more bikes thru the next few years. They all rubbed. Best I can figure, is that the plastic/vinyl cured, and moved.
I don't know where any of them are (I may still have them... just don't know where). But I can attest, I have rolled a couple of big rocks around my rear sprocket. One was so big it cracked my sprocket.
You know how it is here in the flat lands..... Paving still hasn't been invented.