Small data point, but had a red eye SAN-LAX-IAH. First leg CPU cleared 36hr before as a Plat, and wanted to get on standby for morning flights for nonstop SAN-IAH, so went to airport early morning. Gate agent saw the PZ fare class on first leg, and confirmed me into PZ directly on the nonstop SDC. Economy fully booked and only 2 available PZ at the time.