The arbitrariness of the municipal boundaries that drive much of the historical core city and suburb analysis does indeed create significant problems. We commented on this in PERSPECTIVES ON URBAN CORES AND SUBURBS (http://www.newgeography.com/content/002123-perspectives-urban-cores-and-suburbs).
We concluded: "An eventual more precise analysis of urban cores and suburban trends will be welcome. Yet, as our analysis of trends in New Jersey indicated, even the growth in more urban core oriented municipalities was minuscule compared to the state's suburban growth. Further, much of the urban core growth in the nation came from areas that, although formally located within “city limits” actually were on the suburban fringe. This was true, for example, in Kansas City, Oklahoma City and even Portland. This suggests that the small share of growth reported in urban cores would be even less if it were based on census tract data; and suburbanization, as a way of life, may indeed be even more prevalent than this year’s numbers suggest."