everyones freaking out about Raikage having a new arm on page #16 on the latest release.
it seems kinda obvious that he doesn't have the arm on page 14 when he counters Muu's punch.
Then on the very next page, Tsunade does her Yin Seal Release Genesis Rebirth technique to heal her an Raikage after their teleportation:
This is because the regeneration is necessary for the Raikage or Tsunade to survive the teleportation.
specifics on yin seal release:
This "Creation Rebirth" or "Genesis Rebirth" Technique that Tsunade used to heal them after their transportation also regenerated the Raikage's 2nd arm back. the technique is the highest form of Medical Jutsu and even considered to be "The absolute pinnacle of medical ninjutsu", so if any medical technique could regenerate Raikage's arm, its "Creation [Genesis] Rebirth".
Its not a manga mistake. its part of the storyline. Papa's got a brand new bag, and Kage's got a brand new arm.
Personally im stoked, i was so disappointed when he lost it to Sasuke, and at the rate Orochimaru and Tobi get new arms i figured a Kage would have to get his arm back eventually.