A custom home is designed based on the lot it sits on. It is also defined by the fact that it is truly unique and one of a kind. It is especially designed to meet the specifications of the client who commissions the construction.
There was a home that recently sold in Old Agoura that was one of several in the area constructed from the identical house plans. The homes are not distinguishable from each other except for their respective locations.
It probably doesn't matter to the buyer that the home has many "twins" in the same town. The situation does bring up the question however; a seller should be careful when presenting his home as a custom home, especially if he is aware that the home is one of several and by definition, not custom.
There was a lawsuit recently filed by a homeowner who thought he was buying a unique, one-of-a-kind home. He happened upon an identical property that had been constructed using the same house plans. The seller did not know about the existance of the other home yet was found quilty of misrepresentation. The architect also sued for copyright infringement, claiming that he did not authorize the copy-cat home.