@Professional Guest Yes. That's exactly what has happened. I'll get the email that says "if you take one of these, we'll give you whatever you want next month", I'll actually take multiples of what they need, and then the next month, when I email them after I put in my application, I won't hear anything. Or I'll say, "Sure, I'll take these four! I've also got a pending application for next month!" and they'll acknowledge the four I took, but nothing about the pending app.
This has happened a couple times. I honestly enjoy the assignment, because it's a nice outing for my guest and I, so I don't get too angry, but that they can't be bothered to acknowledge that I helped them and give me my choice the following month is really annoying. If they emailed and said, "Sorry, that's assigned already" or "You're not yet qualified for that by our internal metrics", it'd be fine. But I haven't even gotten that courtesy.
Sure, I could stop working for them, but I do occasionally like their stuff. Even when I'm "helping" them, I definitely am not going out of my way or rescheduling anything to do it.