Why 536 A.D. instead of 538 A.D.?

Since the 1260 days (years) prophecy began in 538 A.D. of Papal supremacy, then why would 536 A.D. be the worst year to be alive
due to natural disasters?

Well the edict that placed the Pope as head of all Christendom was issued in 536 A.D. by Emperor Justinian. 

But the Pope was held up for over 2 years in Rome trapped by the Ostrogoths.

It was not until 538 A.D. that General Belisarius relieved the siege of Rome and informed the Pope of his new status and gave him the edict.

Q: So was all this that befell the earth in 536 A.D. a sign from God of the DARKNESS about to befall the earth or just a coincidence?
And he shall speak great words against the most High, and shall wear out the saints of the most High, and think to change times and laws: and they shall be given into his hand until a time and times and the dividing of time. Daniel 7:25

 "In the year 536, daylight itself went away.
Across Europe, the Middle East and parts of Asia, people looked up and saw a sun that gave little warmth and cast a strange, weak light. Summer brought snow in China. Crops failed virtually everywhere, spreading hunger worse than any plague. Then, only a few years

later, an actual plague arrived to top things off. We know from written sources that there were serious drops in temperature, both in Europe and in China. For historians and climate scientists, 536 has become a leading candidate for the worst year to be alive.
The fabled year 536 AD was in the middle of a literal Dark Age.

Byzantine historian Procopius, writing from Constantinople, described the world around the year 536 in which “the sun gave forth its light without brightness, like the moon, during the whole year.” The Roman statesman Cassiodorus later wrote that “the sun seems to have lost its wonted light and appears a bluish color.”

Irish chronicles recorded “a failure of bread from the years 536–539.
“There’s a kind of feedback loop in the problems … Once you get one sort of catastrophe in the pre-modern world, it often leads to other

ones,” Dr. Pattenden said.

Then came the plague.
The damage was enormous and the economy across Europe and large parts of Asia was likely in a ruinous state.
“To put it in some perspective, if you were a carefree 18-year-old in the summer of 535, you’d probably have to live between 80 and 100 years to get back to conditions that were similar to what you’d remember from being a child,” said Pattenden." 

ZMEScience