ASEC: social security income from INCUNERN (prior to 1968)

I’m trying to get social security income over time (1962-2022) but it seems that social security income prior to 1968 is counted in the INCUNERN variable, which includes income from non-wage, non-business, and non-farm sources. Is there a way I can get the amount of social security income from INCUNERN? I see that there’s the GOTSS variable that specifies if a respondent received any social security income but I don’t think I could distinguish social security income from other sources in INCUNERN.