Talking about the PC type of match (9 or 18 holes):
The match play list only contains rated Matchplay, that means that practice rounds like head-to-head and "rooms" games do not count in.
The players listed by name are those from your friend list, and I have yet to hear about a limitation in the match list.
Probably, the new players that you miss aren't your friends yet - they only appear in the summary by tier. Dunno which influence that "255" margin in the friends list may have here.