P.S. to my reply #8.
A tree on roegenealogy.com has Alicia de la Pole, born in Wingfield, Suffolk, parents John de la Pole and Elizabeth Plantagenet. A note says he was John de la Pole of Hartington.
'Notices of the Family of Pole or de la Pole, of Derbyshire, and of other families connected with it'
This suggests a mistake in another source.
'John de la Pole of Newborough, County Stafford, married daughter & heir of Hartington, Co. Derby and had issue Sir John de la Pole of Newborough, knight ...'
This son, John had a son, Peter, whose son was John de la Pole, esquire, of Hartington.
'De la Pole of Hartington … little is recorded of their descent … only pedigree we have met with of them, and this is imperfect, is in Newton's MSS, to which we have been able to make trifling additions from other authorities, still it is very scanty ….'
Then follows a genealogy of the de la Pole family of Hartington. This has a line of John, son of John, son of John &c. One John de la Pole, knight had a son, John de la Pole, esquire, who married Jane Okeover, daughter of Hum. Okeover of Okeover, esq. According to this tree they had 2 daughters, Lucia and Alicia. Alicia's husband was John Daykyns of Biggin Grange, parish of Hartington. There are no dates on the tree. The writer of this text mentions doubts as to whether Alicia was Lucia's sister or her aunt.
Reference is made to documentary evidence that Hartington was already in possession of the de la Pole family in the reign of King Edward IV.
There is a pdf of relevant pages but my link didn't work.
If the genealogy of de la Pole of Hartington is correct, then it seems to me that someone has confused John de la Pole of Hartington, father (or possible brother) of Alicia de la Pole with the John de la Pole, Duke of Suffolk, who was married to Elizabeth Plantagenet, sister of King Edward IV.
To confuse matters further, Margaret Plantagenet, Duchess of Salisbury, daughter of George, Duke of Clarence and niece of Edward IV and Richard III, was married to a member of another Pole family. Henry VIII had her beheaded.