Where do 10 penalty strokes come from?
Shot to 17th green =1
Shot on wrong green =1
2 penalty strokes for breach of 25-3= 2
2nd shot on wrong green = 1
2 penalty strokes for breach of 25-3 = 2
8 strokes to this point + whatever number of strokes to hole out from correct place having taken relief from wrong green.
In my view, you take where the ball lies after the 2nd stroke on the wrong green as your reference point for then correctly taking relief from the wrong putting green - in this case the hole
The next time you [speaking generally, not of Colin specifically] hear someone complaining about there being too many Decisions, you should consider the scenario in this thread as it was covered explicitly by Decision 25-3/2 before that Decision was Withdrawn, purely to reduce the number of Decisions, in 2010. Here's what it said:
25-3/2 Player Makes Several Strokes on Wrong Putting Green
Q. In playing the 4th hole, a player plays his second shot onto the 7th green, believing it to be the 4th green. He marks the position of and lifts and cleans his ball. He then holes out in two putts on the 7th green before he is advised of his error. What is the ruling?
A. In equity (Rule 1-4), the player incurs no penalty under Rule 18-2a for lifting his ball in play without authority.
In match play, the player lost the hole when he made the first stroke on the wrong putting green -- Rule 25-3.
In stroke play, Rule 25-3 does not contemplate a player making more than one stroke from the same wrong putting green. In equity (Rule 1-4), the player incurs a total penalty of two strokes under Rule 25-3. The two strokes made on the 7th green would count toward his score on the 4th hole.
When taking relief under Rule 25-3, the player would use the final location of the ball (in this case the hole on the 7th green) as the reference point for taking relief.
The same answer would apply to other areas on the course from which play is prohibited (e.g., ground under repair from which relief is mandatory or environmentally-sensitive areas).