I see that the variable incalim is not available in the 2015 ASEC-CPS sample. Why is that the case?
In 2014, the CPS redesigned its income questions. 5/8ths of the 2014 ASEC sample still received the old income questions, but the other 3/8ths received the updated questions (see here for more info). The updated questions no longer include a separate question for alimony income amounts. Instead, total alimony income is rolled into the Other Income category.
In 2015, the CPS transitioned completely to the redesigned ASEC income questions; however, respondents are now allowed to designate alimony as the source of “other income.” As a result, it should still be possible to identify at least some alimony income in the source NBER data using the OI_VAL amounts for respondents with OI_OFF=“20: Alimony”. You can then sequentially merge the NBER data with your 2015 IPUMS data extract (i.e. first NBER observation matches to first IPUMS observation, second to second, etc.), verifying the merge using values of sex, age, and race.
Hope this helps.