Savvy mileage earners have known for a long time that the lower level awards are difficult to find, with only a few seats available on each flight.

One game, which I suggest to clients regularly, is when you know dates long in advance, as in a year in advance, call or go online when the seats first open up — 331 days in advance.

On the rare occasions when I personally know dates that far in advance, I practice what I preach. A few Decembers ago, this strategy actually got us tickets to a South America cruise over the holidays. (Although in one direction one flight option literally sold out while I was on the phone with the airline agent.)

I also advise anyone looking for an award to try calling as opposed to just using the website. A good airline reservation agent who can be creative is well worth the additional fee, and may be much better at finding space with partner carriers.

In any case, now that most carriers offer one-way awards, the process is in theory even easier — there’s no need to wait until 331 days before the return flight is available to make reservations (Previously, travelers with longer trips were particularly out of luck, because, for example, an outbound flight would almost certainly be sold out by the time the return was bookable.)

Yet, recently I’ve been hearing from Consumer Traveler readers and clients alike that the lower mileage awards are almost impossible to get, even with maximum notice.

My experience this month bears that out. Three-hundred-and-thirty-one days in advance, at midnight, as soon as I saw flights pop up in United’s computer, I called for flights to Europe in July 2012.

On the outbound, two weeks ago, there were ZERO seats from San Francisco to Madrid on United or Continental, but an agent did find two seats on Lufthansa. So far, so good.

On the return, absolutely nothing. An agent found one seat, again, within two minutes of the flights first appearing, and another agent found flights back from Rome as far as D.C. only.

From D.C. to San Francisco? Nothing at any time for 24 hours, even with a connection, even though the agent told me that the flights had no seats sold.

Both agents suggested “call back,” which I will do, but for anyone who plans in advance, it’s a frustrating situation. Because, the seats, if and when they appear, will vanish quickly.

Clients in our office planning a safari for 2012 finally gave up with using American miles, as both American and British Airways flights were not available, even though they tried every day for a week.

And it’s not just exotic destinations. A reader emailed me to say that he had found next summer 11 months out there were no saver seats from the west coast to Chicago.

Now, maybe seats will be added, maybe not. The airlines will come out with general data about the number of free seats they “give away,” but it’s hard to know how many are at lower levels. At this point too, there’s no way of knowing if some flights ever have any award seats.

And yes, I know, free is free, and beggars can’t be choosers. But when airlines make such a huge deal of mileage programs (and the credit cards that go with them), then it feels like a bit of “bait and switch” not to offer any seats except at the highest levels.

Of course, this sort of post is apocryphal, and yes, some people do manage to cash in miles without a lot of hassle. But I’d love to hear from Consumer Traveler readers. Are you finding it increasingly hard to cash in miles for free tickets? If so, is it affecting vacation planning or your loyalty to a carrier? Please share your stories in comments.

Photo: ©Leocha