Changes

Since the Heike is a war tale and has been shown to be fictional at times, I'd lean toward the 1164 date. Since the Heike largely portrays Kiyomori as a lout, thug, and villain, that could also be a reason why they ascribed this to Tadamori-showing Kiyomori doing something positive and pious would be at odds with the flow of the narrative.

Since the Heike is a war tale and has been shown to be fictional at times, I'd lean toward the 1164 date. Since the Heike largely portrays Kiyomori as a lout, thug, and villain, that could also be a reason why they ascribed this to Tadamori-showing Kiyomori doing something positive and pious would be at odds with the flow of the narrative.