Calling what is nothing but a depository account for SS receipts the TF is just another government slight-of-hand. Normally something put in a TF will be there for a significant period of time.
The residual left in the TF is nothing but the non-negotiable, promissory notes from the US government.
And, it is correct to say that current SS benefits are not paid out of any TF, even if the feds choose to call the SS depository account a TF. The TF is composed of the surplus SS receipts over the decades, which were spent and replaced with promissory notes.
What you've described very clearly is government accounting games and a misnamed depository account for SS receipts and disbursements.
The non-market, interest bearing T-bills in the SSTF and other government trust funds like HI, federal pensions, etc. are included in the $14.3 trillion national debt under "Intragovernmental Holdings" as distinct from the public debt, which is about $10 trillion. Yes, the IOUs do represent an unfunded liability just like the ones in the public held debt. Both have the full faith and credit of the USG behind them. The difference is that the trust fund IOUs must be redeemed by the USG. They are not real assets in the sense that we could sell them to China or they can be transferred to another owner.
The trust funds are a vehicle to maintain the fiction of these entitlement programs. There are laws that say once you use up all of the IOUs, benefits must be cut to reflect revenue. So even if all of the IOUs in SS are exhausted, benefits would still be paid out of the revenue stream.
What you've described very clearly is government accounting games and a misnamed depository account for SS receipts and disbursements.
CBO: Trust Funds and Measures of Federal Debt
"The federal government uses several accounting mechanisms for linking earmarked receipts (money designated for a specific purpose) with corresponding expenditures; some of those mechanisms are trust funds (such as the Social Security trust funds), others are special funds (such as the fund the Department of Defense uses to finance its health care program for military retirees) or revolving funds (such as the Federal Employees Group Life Insurance fund). Although trust funds are designated as such by law, there is no substantive difference between trust funds and the other types of funds.
When trust funds and other government funds have receipts in excess of amounts needed for current expenditures, they are credited with nonmarketable Treasury debt known as government account series securities. At the end of 2009, about $4.3 trillion in such securities was outstanding, mostly credited to the Social Security trust funds. (That amount can serve as a measure of how much receipts, including interest, have exceeded outlays over time for the programs financed through those funds.) The value of the outstanding securities (that is, the debt held by government accounts) is combined with the amount of debt held by the public (described in Chapter 1) in two measures of the government’s debt: gross federal debt and debt subject to limit.
In total, the federal budget has more than 200 trust funds, although most of the money is credited to fewer than a dozen of them. Among the largest trust funds are the two for Social Security (the Old-Age and Survivors Insurance Trust Fund and the Disability Insurance [DI] Trust Fund) and the funds dedicated to Medicare’s Hospital Insurance (HI) program (also known as Part A), civil service retirement, and military retirement.
When a trust fund receives payroll taxes or other income that is not needed to pay benefits immediately, the Treasury credits the fund and uses the excess cash to reduce the amount of new federal borrowing that is needed to finance the governmentwide deficit. That is, if other tax and spending policies are unchanged, the government borrows less from the public than it would in the absence of those excess funds. The reverse is the case when revenues for a trust fund program fall short of expenses. Thus, the balances of trust funds are not a measure of resources available to pay future obligations for the respective programs; those resources will need to come from federal revenues or additional borrowing in the years those obligations are due.