Do you have a micrometer or pair of calipers? If so, can you make some measurements?
You are seeing ferrule stations. The manufacturer deliberately added material to strengthen the blank. This was common on Garcia Conolon rods with the metal spigot ferrules (although the decorative ferrule wraps mask the increased blank diameter). The increased material also creates a stiffer spot in the rod taper.
As you can see in the photo below, early graphite used sleeves to strengthen the ferrule area. Tip over butt ferrules often had extra material over the female portion. Because graphite blanks have such thin walls the thickness increase is sometimes hard to detect by eye.
I have three, uncut, 9-foot, graphite blanks in the rathole. They have very distinct ferrule stations for cutting the rod into a three piece. If the original rod designer thought the ferrule stations were a good idea, I am not going to mess with them.
Thom