QUOTE(sbguard9 @ Jul 7 2008, 03:58 AM)

There is no rule against picking the last two 9's to add up as your official score. There absolutely no problem with that. That's a 79, congratulations. BUT if you really feel like your score isn't justified there are two ways to post an incomplete round. In other words if you take the score from the first two nines and then just have a third and incomplete round score, you can
a.) estimate what your score would have been if you played in a similar or average way on the second nine, or
b.) complete the other 9 holes later. If you do this all you have to do is go play one of the other two nine holes at the same course and shoot 41 or better to break 80.
On A, post the 9 hole score, not an 18 hole estimate.
On B, two nine hole scores can be combined from different courses.
Here's section 5-2d of USGA Handicap Manual:
QUOTE
d. Treatment of Nine-Hole Scores
Once posted, a nine-hole score will be treated as follows:
(i) Nine-hole scores must not be designated as T-Scores;
(ii) When two nine-hole scores are combined, the USGA Course Rating is the sum of each nine-hole USGA Course Rating and the Slope Rating is the average of the Slope Rating of the two nines (if the average is .5, it is rounded upward to the next whole number);
(iii) Two nine-hole scores combined to create an 18-hole score should be designated with the letter C (e.g., 85C). If either of the two nine-hole scores was posted via Internet (See Section 5-2a(vi)), the score should be designated CI;
(iv) Nine-hole scores are combined in the order that they are received into the player's scoring record from any club or from any combination of nines, regardless of score type. For example, a front nine middle tee score could combine with a front nine back tee score made from any course.
An 18-hole score created by the combination of two nine-hole scores will display the date and course name (if applicable) of the latest nine hole score (e.g., April 29 and May 4 = May 4).
A nine-hole score will be retained for combination with another nine-hole score until it is older than the twentieth oldest eighteen-hole score in the scoring record, and nine-hole scores will be combined in the order they are received in the player's record, and "not necessarily by date."