Teaser 2423: [PIN combinations]

From The Sunday Times, 1st March 2009 [link]

Joe could not remember his six-digit PIN, but he did remember that it used the digits 1 to 6 in some order. He tried the following four without success:

6 1 2 5 3 4
4 6 5 3 2 1
2 3 4 1 6 5
3 2 6 5 4 1

Actually, more than one digit in each of these numbers was in the correct place. Had Joe known this, he would have needed to try only a few more numbers to find his PIN.

How many more numbers did Joe need to try?

This puzzle was originally published with no title.

[teaser2423]