With my 2 fer 1 ticket, how does Disneyland know that I have already entered to one of the parks?

Question

With my 2 fer 1 ticket, how does Disneyland know that I have already entered to one of the parks?

Answer 1

Every ticket has a unique Bar Code.  Their ticketing and attendance systems knows which park(and when) you entered first based on that bar code.  So if you attempt to use it at the same park again the Cast Member at the entrance will kindly tell you that you can't use it at the same park for both days.

It may be too late to upgrade this ticket since you had to use your first day by today for the 2fers.  But if you really wanted to go to both parks on the same day(or the same park twice) you could have bought the 2fer Park Hopper for $91 and been able to do that.  This would have given you a 2 day Park-Hopper for the price of a 1-Day park hopper for non-residents.