What is included in the INCSS variable?

For INCSS: Q: to be clear, this does or does not include Supplemental Security Income (SSI)? I pasted the definition below for convenience.

INCSS reports how much pre-tax income (if any) the respondent received from Social Security pensions, survivors benefits, or permanent disability insurance, as well as U.S. government Railroad Retirement insurance payments, during the previous year.

Social Security and Supplemental Security Income (SSI) are two different federal entitlement programs (see this factsheet for further details). INCSS reports Social Security income and Railroad Retirement benefits for railroad workers who do not participate in Social Security; it does not does not include SSI. Instead, INCSUPP is used to report SSI income in the ACS/PRCS samples as well as the 2000 census. The questionnaires in each of these samples include separate questions about Social Security and Supplemental Security Income. In the decennial census samples prior to 2000, SSI income is reported in INCWELFR.