Any date prior to September 14, 1752 is speculative

See: The British Switch to the Gregorian Calendar
The year of 1752 began on March 25th and ended with December 31, 1752, thus the earlier days of 1752 never existed, as the deleted days of September 2--13 also never existed.

A new manifesto to revise prevailing history and chronology
The French Revolution from 1788/89 might just be the first historical narrative that is credible. But any historical events before this time are impossible to confirm. Any attempt to set up and describe a year such as 1700 in historical terms is absurd. The creation of historical forgeries and fabrications has always gone hand in hand. Before the beginning of the 19th century nobody was interested in writing true history.

In this post, I state a theory, which should be able to be proven or disproven, not something I believe in 100%.  Are there any original documents (e.g. a letter from a king) that have a written date prior to 1752?

Obviously, people and documents and events existed prior to this date, but the dates at which they lived were assigned after this time by historians and archaeologists and such.  When did "reliable contemporaneous written history" begin?  There probably are such documents prior to 1752, but how far back?

WE DISCOVERED THAT THERE IS A DISTINCTLY DEFINED BOUNDARY IN HISTORY – THE FIRST HALF OF THE XVII CENTURY. We know more or less what happened after this point, i.e. closer to our time. In any case, beginning with the end of the XVIII century. But we have a very poor knowledge of what took place prior to the middle of the XVII century [i.e. 1650]. This border line appeared artificially. It is not a result of the natural forgetting the information. It separates the accurate chronology from the incorrect one.  http://chronologia.org/en/how_it_was/preface.html

The first comprehensive English dictionary was "A Dictionary of the English Language" prepared by Samuel Johnson.  It was published on 4 April 1755.

Update: The first version of the Encylopedia Britannica was published in 1768 in Edinburgh, Scotland.

There was a world war lasting between 1754 and 1763 called the Seven Years War in Europe and the French and Indian War in the New World.

King George II of Great Britain, who was king from 1727 to 1760, was born in Germany.

In Russia, Pugachev's Rebellion occurred in 1773-1775.  It was really a civil war against Catherine the Great, who was Empress from 1762 to 1796 and had a dubious claim to the throne, and who was born in Germany.

Update 2:  A massive earthquake, tsunamai and fire on November 1, 1755 destroyed Lisbon, Portugal.  This was seen as punishment by God and it was a major factor in the downfall of the Portuguese Empire (which however didn't finally end until giving Macau to China in 1999).

Update 3:  The War of the Austrian Succession (German: Österreichischer Erbfolgekrieg, 1740–1748) involved most of the powers of Europe over the issue of Archduchess Maria Theresa's succession to the Habsburg Monarchy. The war included peripheral events such as King George's War in British America, the War of Jenkins' Ear (which formally began on 23 October 1739), the First Carnatic War in India, the Jacobite rising of 1745 in Scotland, and the First and Second Silesian Wars.