An acquaintance pointed me to the NBER May CPS data extracts for the union variable going back to 1973, but I have been unable to find it in the IPUMS-CPS database before 1984. Is that something IPUMS has coded? If not, do you have any ideas on how to potentially merge this data into a CPS extract, or is that not possible to your knowledge?
At the present time, the UNION variable in IPUMS CPS is only available back to 1984. You can, however, merge NBER data with IPUMS CPS data together. We have a blog post that discusses some of these details. In particular, you can use the variables HRHHID, HRHHID2, HUHHNUM, HRSAMPLE, HRSERSUF, and LINENO as linking keys while merging datasets. This method is possible because, with the exception of LINENO (which is called PULINENO in NBER files), these variables have the same names in IPUMS CPS as in the raw CPS files available via NBER. After the merge is completed we suggest to confirm everything worked properly by checking that the sex, age, and race of respondents match between the datasets.