Marriage plans for Mary of York

I've read that in the 1475 Treaty of Picquigny Mary was the reserve to marry the Dauphin Charles if her elder sister Elizabeth died.

I've now read in Amy Licence's biography of Elizabeth of York that at one time there were negotiations for Mary to marry Hans, heir to the King of Denmark but these had been over by 1478 when Hans married Christina of Saxony. Does anybody know when the abortive negotiation for Mary to marry Hans started? Licence doesn't say.

I've then read in an old Ricardian from 1999 about The Royal Burials of the House of York by Anne Sutton and Livia Visser Fuchs that it was planned for Mary to marry Frederick, King of Denmark. It says in Princesses of England by MAE Green on Amazon that Mary had been withdrawn from marrying Frederick because she was ill. However Sutton and Visser Fuchs do not say the marriage plans were off when Mary died in May 1482.

Also Wikipedia says Hans also known as John was King in 1481 not Frederick, but there is something about them being co-Dukes.

So what were the different marriages plans for Mary and when and what was the status when she died in May 1482?

Be very grateful if anyone can clarify the facts.