That makes sense. Then again the Gedo Mazou already had some of the 8&9tails chakra.Because if you look back to when Madara first came to that location, Madara wanted to capture the 8 and 9 tails so he could let the Gedo Mazou absorb them before it turned into the 9tails. When the 10 tails arrived Madara said "Oh well" because it was too late to add the 8 and 9 tails to fully complete the 10 tails.