It's actually a lousy question because it proves nothing. Money is held in different accounts not because they are actually stored in physically different places, but because they are conceptually different, and because the concepts are not fungible. I do not (and in some cases cannot) transfer money between some of my different accounts at my brokerage even though all that money is ultimately in the same pool somewhere.
In the case of the general fund and the trust fund, the trust fund surplus money was not spend in the 90s or at any other time since the surplus started growing again; it remained in surplus, and - counting its interest income - it remains in growing surplus until about 2019, at which point that surplus starts being dipped into until 2034.
(Also note that historically, this has already happened. [1] There was a social security surplus, and then it got spent down partially in the late 70s, and then started growing again in the early 80s. Everyone got their checks.)
Why is this distinction necessary? Again, because the general fund has gone into deficit. People like mason240 try to pretend that it hasn't gone into deficit as much as it has, because the people that are advantaged by the general fund deficit have a higher tax base than the people that have paid into payroll tax (on average). So why do we make this distinction? To protect against the transfer of money from the poor to the rich. Why do people like mason240 insist otherwise? For not other reason than to keep that money, and to weaken social security.
