Inflation adjustment when comparing estimates across time periods

I came across some documentation that when comparing ACS 5-year estimates, the earlier estimate needs to be adjusted for inflation.  See Chapter 10 (USING DOLLAR-DENOMINATED DATA) in the following document:

My question is about this statement on p. 66 of the PDF: “The recommended inflation adjustment uses a national-level CPI and, thus, will not reflect inflation differences that may exist across different geographic areas.” 


I am wondering whether this adjustment still applies since I am using census tract, county, and state-level (vs. national-level) data.  In addition, I’m wondering if there is an issue in using a national-level CPI to adjust lower-level data.