Kirby Inks

Jack rarely inked his own work, especially after 1960 where he was predominantly a penciler, but here is a rare example most Kirby scholars agree was inked by Kirby himself. The cover to Fantasy Masterpieces #4 (1966).

The smaller images at the left and on the bottom appear to be stats taped to the artboard, but this image is original art.

I wonder why out of almost 10,000 pages of artwork for Marvel during the 1960s, this is one of the only images Jack inked. Maybe there was some strange deadline problem, and Jack was in the Marvel offices and quickly added ink to this page?