<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Shareholder:
Some airline res systems will record an award flight for mileage credit if last minute changes are made, such as involuntary rerouting, standing by for earlier flights, etc. This does not occur frequently, but has been known to on occasion. Otherwise, the class of service code award seats are assigned are programmed into res systems to be invalid for mileage credit.</font>
It depends on how you are reticketed. It can be easier to put a reticketed passenger in an ordinary revenue seat, since that's the normal case and therefore the one that systems are generally designed to handle fastest. If there's a line of people waiting (not unusual in situations where reticketing is necessary) the agent may not want to go to the extra trouble of rebooking the seat as an award.
A similar situation can occur when upgraded economy is reticketed. You shouldn't get a class of service bonus, but you will sometimes be reticketed as paid F or J and get it.