If there is, what is the maximum number of clues of a pattern that has only 1 valid sudoku?

For instance this sudoku is interesting:

- Code: Select all
`1 . .|. . .|. . 2`

. 3 .|4 . 5|. . .

. . .|. . .|6 . .

-----+-----+-----

. . 5|. . .|7 . .

. . .|3 . 8|. . .

. . 6|. . .|2 . .

-----+-----+-----

. . 2|. . .|. . .

. . .|9 . 1|. 3 .

7 . .|. . .|. . 4

If you change the values of up to five clues and get a valid sudoku, then the sudoku obtained is isomorphic to the starting sudoku, though I have not proved yet that this pattern has just a valid sudoku.

I'll do a research on gordon's list to see if I can find anything interesting.

Addendum: In gordon's list of 17's there are a lot of patterns with a unique sudoku.