Good start.

You nearly got me with the Sumer Is Icumen In, Greg ... had me sweating for a while. The 4 part harmony thing was just tongue in cheek, so I checked the original manuscript and there's only the melody line. It's polyphonic because it's a round. Here's my notes for yours ... good work.

600-700 - TRUE. Caedmon was attached as a labourer to the double monastery of Whitby (Streoneshalh), founded in 657 by St. Hilda. The story given by Bede is that one night, when the servants of the monastery were gathered about the table for good-fellowship, and the harp was passed from hand to hand, Caedmon, knowing nothing of singing or poetry, left the company for shame, as he had often done, and retired to the stable, as he was assigned that night to the care of the draught cattle. As he slept, there stood by him in vision one who called him by name, and bade him sing. "I cannot sing, and therefore I left the feast." "Sing to me, however, sing of Creation." Thereupon Caedmon began to sing in praise of God verses which he had never heard before. Of these verses, called Caedmon's hymn, at least 3 versions survive in Old English.

1200-1300 - TRUE. There had to be one really easy one. There's a copy of the manuscript online here along with some notes, summarised here. British Library, MS Harley 978, is a manuscript from Reading Abbey dating from the mid-thirteenth century. Reading Abbey, however, did not have a scriptorium, and the MS was probably copied at Oxford. It was probably owned by one of the three Reading monks it mentions, William of Winchester, a lover of music whose history was otherwise undistinguished and occasionally scandalous; on a visit to Leominster Priory in the 1270s, he was brought before the Bishop of Hereford for incontinence with a number of women, including a nun of Limebrook Priory. The manuscript is a miscellaneous compilation, mainly of Latin and French texts, useful or entertaining rather than devotional; it includes other musical pieces (all religious), medical material, Goliardic satires, the earliest and best text of the Lais of Marie de France, and a French poem on hawking. Sumer is icumen in is the only Middle English text in the manuscript, and it is possible that it was included primarily for its musical interest.

1600-1700 - FALSE, though it says so on this site! "The Virginia Reel" is an American variation of the English dance "Sir Roger de Coverley". The dance first appeared in the 1695 edition of Playford's "The Dancing Master" under the title "Roger of Coverly". Following the appearance of the popular fictional character, Sir Roger de Coverley (Addison 1711), the name was subtly changed (though never in Playford). How the fiction got about is explained in a footnote here. See here for details of the Playford dance.

1700-1800 - TRUE. John Gay's Beggars Opera was not an opera in the usual sense of the word, but rather a "Musical". More information here.

Mr Happy ... fine so far, but is it true? and why?

:-)