Golfer Z is a real person but not me. Of his last 20 scores, 9 were tournaments and 11 were non-tournament. His handicap is primarily determined by his tournament play as his casual play tends to be outside his 10 best differentials. These results are consistent going back several years. His handicap index floats between 13 and 10. In the north central US we tend to have our indexes increase in late Autumn (aeration, poor weather, colder temps, etc ...). As we start in Spring, the index may increase a bit more and then start to decrease as the weather and conditions improve and we re-find our swings. His index follows this pattern and there is no reason to think he intentionally pads it.
He plays against 20-25 people of similar handicap. Each player gets his full course handicap. Player Z is in the money (top 5) 75% of the time and every year for the past 5 years he wins the most over a 12 tournament schedule or is at least in the top 5 compared to our club's 150 members.
Fortunately, I am never in his flight and my interest is mainly academic. If the handicap system works and levels the playing field, in theory one player should not consistently have a better "net" record, all other things being equal. Of course, the handicap system can't capture that unique competitive ability some people have. Maybe he is just one of those people for whom everything slows down during the heat of competition and he rises to the occasion.
It seems like the consensus is there is nothing going on other than some timely play on Player Z's part. Thanks for the feed back. Sorry about all the choices in the poll. I will do better next time.