In all seriousness, I find it very confusing that both visually or logically that DF-41 and DF-61 are almost the same thing in every aspect, the only different I spotted so far that their codenames were painted in different area on their bodies.
Between DF-41 and DF-61, I can imagine the difference is better carbon fiber and propellant with perhaps different warhead layout however the reason behind it remains unknown.
Meanwhile DF-31B looks completely different than DF-31AG in diameter of canister, the commentator goes as vague as possible on it and one of the interesting points is that the official commentator labels "DF-31" as new missile after others.
We can go further on the line once we have more clues about
1. What exactly DF-31B contains in its canister? Missile with Warhead? Only missile? Only booster without PBV?
2. What makes them change DF-41 to DF-61, instead of DF-41A?
3. Where did DF-51 go?