As you have discovered, there are a number of different resources for examining occupations across years of the ACS that include a change in the occupation coding scheme.
- Microdata files: The 2006-2010 5-year and 2008-2010 3-year ACS microdata files code respondents’ occupations based on the year data was collected. Records with MULTYEAR < 2010 are based on the 2000 SOC (which inform the 2000/2002 Census Occupation Codes) and those with MULTYEAR = 2010 are based on the 2010 SOC (which inform the 2010 Census Occupation Codes).
- Summary files: The excerpt that you cite notes that for the creation of 2006-2010 summary tables that bridge this change, Census Bureau experts reassigned the occupations of each respondent interviewed in 2006-2009 to a new 2010 code. We provide these types of Census summary tables on our spatial data project website, IPUMS NHGIS.
- Crosswalks: The Census Bureau produces a conversion rate crosswalk that allows researchers using the microdata to see the estimated percent of people in each old occupation code (e.g., 2000/2002 Census Occupation Codes) who would be assigned to each new code (e.g., the 2010 Census Occupation Codes). The comment in this IPUMS CPS guide to occupation code changes notes that this conversion rate crosswalk is available for comparing the 2008 and 2010 data in reference to analyses of the 2008-2010 3-year ACS microdata file. Note that I can no longer find this 3-year crosswalk on the Census Bureau’s website.
On a related note, it is unclear to me which years of data the conversion factors are based on; I was not able to find detailed documentation on this. I assume that the factors in the 3-year crosswalk to use data from 2008 and 2009 to calculate conversion factors for 2010 occupation codes. However, the Census Bureau also provides a document with conversion rates using the 2006-2010 5-year file on its Industry and Occupation Code Lists and Crosswalks page and the values in that document appear to be identical to those for the 3-year crosswalk. While I would expect the conversion rates to be similar overall, I would expect minor differences when using two additional years of data. You may want to reach out to the Census Bureau to determine the basis used for these values. Your interpretation of the note regarding the 2012-2018 crosswalk makes sense to me.