"1. It is based on T (tournament) scores only. An average golfer gets in only 3 to 5 scores a year. This makes the system very slow to respond to current ability. The time late in detecting changes in ability is often six months, which Dr. Fran Scheid found in a study years ago. It simply does not keep pace with current skill."

The above quotation is in line with how my friends in Scotland calculate handicap. I know at least a dozen through working in Scotland. They all seem to follow the above rules.

Perhaps there are some "exceptions" to the way it's done?