Crazy Knights sequential move puzzle

Sold Out 1999 Limited Edition set of 12.
Original Price: AU$90 (about USD58 at the time)
In April 2007 one of these puzzles sold at Baxterweb Puzzle Auctions, Featuring the John Ergatoudis Collection Phase 12 for USD 281.00.
And another was sold in January 2015 for USD296.00

The puzzle is to exchange the positions of the two white knights with the two black knights. The starting positions of each knight are inlaid on the board.

You must stay within the squares on the board and may use ‘Knight’ moves (as in chess) only. It was thought this puzzle was devised in Russia, but recent advice is that its origins are unknown. However, it was adopted and further developed into its current form by Ili Kaufmann in Israel. It was presented by Edward Hordern at the “Gathering for Gardner, Three” in January 1998.
The board is made from Queensland Spotted Gum. The knights are cast from pewter. The bases of the white knights are Queensland Silver Ash and the black knights are Blackbean.