When establishing a Handicap Index, how are 9-hole scores treated?

Handicap Index, 9-hole scores

To establish a Handicap Index, a player must play and post a total of 54 holes, which can be made up of 9-and / or 18-hole scores. The use of expected score does not come into play until a golfer plays and posts 54 individual hole scores. 

Once the player has posted scores from a total of 54 holes and an expected score can be determined for the player, an 18-hole Score Differential will be calculated for each 9-hole score and displayed within their scoring record. At this time the player will have established their initial Handicap Index.