Warbeck
2 of the 7 encyclopedias on this shelf carry an entry for Warbeck. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
Perkin, a pretender to the English crown. He was born in Flanders, it is thought, the son of a Jew. He became attached to the court of the Duchess of Burgundy, where he was taught to represent Richard, Duke of York, one of the lads whom King Richard is accused of having caused to be murdered in the Tower. Warbeck was encouraged in his pretensions by Charles VIII of France and by the Scotch. He made an unsuccessful landing in Kent in 1495 and invaded England by way of Scotland in 1496. In 1497, using Ireland as a basis, he landed in Cornwall but was captured and confined in the Tower. He was tried for high treason and was hanged at Tyburn in 1499. Warbeck has been made the subject of several tragedies, the most important of which is that by Ford. It was presented in 1633 under the title of The Chronicle History of Perkin Warbeck.
Collier's New Encyclopedia (1921)
or OSBEC, PERKIN, a pretender to the English crown; was the son of a Flemish Jew, and was set up by Margaret of York, Dowager- Duchess of Burgundy, as claimant of the crown of England against Henry VII. For this purpose she recognized him as her nephew, Richard Plantagenet, Duke of York, the younger of the two princes who were murdered in the Tower by Richard III. He was patronized by France and Scotland, married a kinswoman of the Scotch king, James IV., made several fruitless invasions of England and Ireland, was taken prisoner after an attempt on Cornwall (October, 1497), and confined to the Tower, where, his plotting being continued, he was executed, Nov. 23, 1499. Vol. X