1. The True Tragedy of Edward of York: The third part of Shakespeare's Henry VI first appeared in print in 1595 in an octavo edition titled The true Tragedy of Richard Duke of York, and the death of good King Henry the Sixth.
2. Rampaging Northerners: After defeating the Yorkists at Wakefield, the Lancastrian army charged south to free Henry VI and left a sizeable amount of damage behind them, to the extent that the citizens of London refused them entry and even stole food from them before opening their gates to Edward's army coming from Wales.
3. The Holy Trinity: One of the anonymous London chronicles gives Edward the following speech -- 'Beethe of good comfort, and dredethe not; thys ys a good sygne, for these iij sonys betokene the Fader, the Sone, and the Holy Gost, and therfore late vs haue a good harte, and in the name of Almyghtye God go we agayns oure enemyes'.
4. Duke Philip is fêting the boys: The Duchess sent her two youngest sons, George and Richard, to Burgundy after the Battle of Wakefield, where, according to a number of chroniclers, they were treated extremely well. Their elder sister Margaret married Philip's son, Charles, in 1468, and the Yorkists were strongly allied to the Burgundians until 1475 when Edward shortchanged them for a more profitable alliance with France.
5. The banner: Edward's royal standard was the rose-en-soleil, and, according to Hall, he chose the sun based on the parhelion at Mortimer's Cross. Also, clock gears look like stylised suns, and Edward was known for being very fond of shiny things.
6. Proper uses for leeks: Fluellen is a character from Shakespeare's Henry V who is obsessed with leeks. We don't know why.
7. Twice the size of Ned's: It has been estimated that the Lancastrians outnumbered the Yorkists by roughly 10,000. However, the chronicle sources are all extremely sketchy and often exaggerate.
8. Humphrey of Gloucester: Henry V's younger brother, he was Lord Protector of England from Henry V's death in 1422 (which left his one-year-old son King of England) until 1447, when he was divested of the Protectorship and died shortly after of undetermined causes. Most sources after 1461 hint that he was murdered by a rival faction.
9. Clifford: Lord Clifford, one of the Lancastrian captains whose father died in battle against the Yorkists in 1455, was commanding at Wakefield. Hall's embellished account of the battle includes a dramatic scene where he avenges his father’s death by murdering York's son Edmund, who, for some inexplicable reason, is depicted as being twelve instead of seventeen.
10. Bilis: Bilis Manger is a minor villain from the first series of Torchwood. We know very little about him, aside from the fact that he can manipulate space and time, and that he's not very fond of Torchwood.
11. An ill-luck name: Referring to Henry of Lancaster deposing King Richard II in 1399 and supposedly laying the seeds for the Wars of the Roses. At least if you believe Shakespeare.
12. Too many shadows: His father was Henry V. Can you blame the man for having inadequacy issues?
13. I'll keep it in mind: See any and all earlier comments about Edward, Hastings, and women. The authors with to state for the record that they really don't make this stuff up.
14. Half-brother Francis: Warwick's half-brother, the Bastard of Salisbury, did die at the Battle of Ferrybridge, but none of the sources give him a name.
15. The majority of this speech is based on Edward's speech before Towton in Samuel Daniel's Civil Wars, VIII.9-12, which, in turn, is inspired by Caesar in Lucan's Pharsalia. Except when it's Hall's Chronicle, f. 86r or Henry V, IV.iii.60-4. That being said, Daniel stole from Shakespeare first, so the authors are merely following in a long and honoured tradition.
16. Henry V, IV.iii.65-6.