harry potter - How could MACUSA exist in 1693 or be in Washington in 1777?

Two brief excerpts from The Magical Congress of the United States of America (MACUSA) By J.K. Rowling on Pottermore state the following:

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  The Magical Congress of the United States of America, known to American witches and wizards by the abbreviation MACUSA (commonly pronounced as: Mah – cooz – ah) was created in 1693, following the introduction of the International Statute of Wizarding Secrecy.

  
  

  
  


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  It was in Washington that President Elizabeth McGilliguddy presided over the infamous ‘Country or Kind?’ debate of 1777.

  
  

  
  

How is this possible since the "United States of America" was not founded until 1776 with the writing of the Declaration of Independence AND Washington, DC was not founded until 1790?

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More to the point how did a team of writers, advisors, editors, etc. not notice this glaring error? Have any comments been made by Rowling or her team regarding this?

Answer

Probably for the same reason MACUSA is called MACUSA in 1693, over 100 years before the United States became the United States, and why Dudley had a Playstation before Playstations existed!

Poor or no research to validate the numbers. AKA Author error.

J.K. Rowling admits to making the occasional continuity error:

"As obsessive fans will tell you, I do slip up! Several classrooms move floors mysteriously between books and these are the least serious continuity errors! Most of the fansites will point you in the direction of my mistakes. But the essentials remain consistent from book to book because the story has been plotted for a long time and it is clear in my mind."

Accordingly, I would like to know for how long J.K. Rowling has had Pottermore planned out.

As well, we all know J.K. Rowling is bad at math.

As of this writing, I cannot find any comments on this matter by J.K. Rowling or her staff.

_{I answered this question solely to use HelloGiggles.com as a source!}