There’s always this option. 
Including the included towns certainly makes logical sense in general, and I’m more than willing to defer to local knowledge on the actual relationship of those towns to Indianapolis. The resulting overlap between Indianapolis and Cumberland is unfortunate, but I already mentioned two common cases where boundaries overlap at the same level (disputes and surveying errors), so maybe we can live with a third class of overlap. At least Nominatim doesn’t suppress Cumberland on the Hancock County side of the county line. We’d still have to document this weird case so that another well-meaning out-of-towner won’t come along and cut it out of Indianapolis. Maybe we can get OpenCage to mention it in one of their epic #geoweirdness rundowns.