city of residence 1 year ago

A city can be identified if and only if its boundaries line up with the PUMA boundaries (or migpuma1 boundaries if I look at the city of residence 1 year ago (MIGCITY1) ). However, some cities (e.g. Akron, OH) are identifiable when i look at the variable CITY but they disappear when I look at the city of residence 1 year ago. How is this possible?

Thank you for your time

Cities identified in MIGCITY1 actually use MIGPUMA1s, which are largely the same as PUMAs, but some have been combined to protect against individual identification. Because MIGPUMA1 is not exactly the same as PUMA, some CITYs are not available in MIGCITY1.

I hope this helps.