[Psycho_Bunny]

I don't know. I've always assumed that when "The Messiah" is printed on a score, it's probably the most likely name for a couple reasons; first and foremost because "ensemble" music copyists tend to be anal about such things - one mistake could ruin a page that took an hour to set.  Scoring is a b#tch.  

Another reason is that often, the most popular scores are the photocopies of 1800s to early 1900s hand-set scores which are not that many generations removed from the composer.  (The most beautiful score I've ever seen is my first printing, hand-set "Also Sprach Zarathustra" - almost any page of which, could be framed and hung.)

I know there has to be a picture of the title page to this piece, in Handel's pen, but I've never seen one.

[Bahbah]

George Frideric Handel - Messiah

I did a Google search and got the above heading off of a website for the Oratorio. I'm supposed to be working so didn't have much time. You might find something of interest. BTW, you are absolutely right about music copyists, so the addition of "The" has always surprised me.