What Do We Know? Origin of a Nursery Rhyme

  i was looking for crafty ideas today and got diverted into nursery rhyme stuff.  Nursery rhymes had come up recently in a baby shower game, and someone mentioned that their origins were rather nasty.
  i knew that they were political and topical to the time of origin, but didn't
remember the stories, so i followed up on a few.
  Yeah, internet wandering.

Historical Background

  i suppose i wasn't too surprised about the gruesome backstory of Mary Mary Quite Contrary.  What surprised me was that one source equated "Bloody" Mary Tudor, daughter of Henry VIII, with Mary Queen of Scots.
  Either i misread that source, or some-other-how i'm unable to trace it now, but the confusion is not unusual.

Pesky Detail

  Boom is fairly knowledgeable about history, and he assured me confidently that there was only one Mary, that Mary Queen of Scots was indeed daughter of Henry VII and the one known as Bloody Mary.

  He actually got our 1958 encyclopedia to settle our difference of opinion - i think that may be the first time he's consulted that.
  How often do we muck about in that era of history anyway?  The lives of these cousins did overlap.
  And even Wikipedia acknowledges that there's confusion over the exact origin of the nursery rhyme, citing Catholicism general, or one Mary or the other as possible inspiration.

The Point

  Well, these little detours are way too much fun.  But what's the point?
  In everyday life, does it matter to us in the 21st century whether Mary Queen of Scots was the same woman as Bloody Mary?  And are our lives really enriched by knowing the horrid details of torture behind those pleasant words?
  Maybe not.
  But it doesn't hurt it's a good habit to be careful about these things.  You never know when the person you're talking to DOES think that pesky detail to be of critical importance.
  And maybe if you're sharp, you won't overlook that little word "not" in the legal document you're about to sign.
  That word that will change everything.

    Want more on Mary, Mary Quite Contrary?  Not pleasant reading, but here ya go:
The Real Meaning of Mary Mary  
A British Site
i did find other sites offering the meaning of this, but none of them offered any possibility other than Henry's daughter.