How to merge IPUMS CPS with IPUMS USA?

I am trying to merge some data from IPUMS CPS and IPUMS USA on year and ind. Most years match pretty well, but 1968-1970, 1980-1982, and 2000-2002 have little to no matches. Does one of the two report ind on some sort of lag? Or is there some other explanation for why they have different ind values for the same year?

For the 2000-2002 CPS samples, the 1990 Census values of IND were used. For the 1980-1982 CPS samples, the 1970 Census values of IND were used. For the 1968-1970 CPS samples, the Census never used similar values of IND. You might consider using a standardized industry variable such as IND1990, rather than IND, to facilitate easier comparisons between samples and over time.

Also, keep in mind that the Universe (USA; CPS) of the Industry variables differs between the two sources. I recommend reading the Comparability tab on the CPS IND variable page for more information on how industry variables differ between IPUMS-CPS and IPUMS-USA.

Hope this helps.