Andrew, I like that statement also... because it is true. However, it may not really be pertinent to this situation. As often happens, the original poster did not clarify the problem very well, and then later came up with additional information. From what I can make of the thread, the lot is not subdivisable with the improvement on it. Therefore, if highest and best use is as improved, the issue of appraisal of subdivision does not come into play.
Additionally, I am under the impression, in Missouri, that only a CG can appraise a subdivision, but that restriction applies only to those subdivisions with more than five lots. I'm pretty sure I'm right about this, but not positive; and, it should be similar in other states. Anyway, to my understanding, there is no restriction on a residential appraiser separately appraising two lots.