GordonGordon to answer your first question, all of our information is live and never cached, it is retrieved in real time as it is searched. We know that the UA inventory especially is accurate as we get the UA data directly from the reservation system that hosts UA.

What your travel agent is telling you isn't that there isn't any inventory in that class, but that there aren't any fares available for purchase in that class. Just because a flight has inventory in H or M class, if there is no corresponding valid, bookable H or M fare then it doesn't matter. Please make sure to compare the availability results with a Fare Information search to determine the valid fares for the dates you'll be traveling.

Also, is your travel agent US based? If not, there is a possibility that UA could be showing non-US travel agents different availability then US based agents. Other airlines are known to do this, however we haven’t heard of UA doing it. Also what GDS is your agent using?