Possibly what they’re doing, now that I think about it, is this: They tell buyers who they’re not sure about that only a couple houses are available. They judge from the buyers reaction (what questions they ask, how interested they seem) whethere they’re a serious buyer. If they judge that they are, then they say, “oh, it turns out that lot 22 is also available. Don’t like 22? Oh, it turns out 57 just came back on.” And so on.
Just a wild guess, really.
Did they ask you which plan you were interested in? If so, were the ones available all that plan? If not, were the 3 that they told you about one of each plan?