I have constructed the conspuma for 1990 and 2000. However, I have found that the conspuma code is not consistent for both years. For example, Los Angeles county is conspuma 47 in 2000 and conspuma 46 in 1990 and Los Angeles city is conspuma 46 for 2000 and conspuma 47 for 1990.
I am doing an analysis at the conspuma level, taking into account the cities/counties which each conspuma contains.
Is there any reason for this situation?