We got some dream fast passes last year on the 2nd May for MK, coming out of HM however we did not need to use them so are still intact , can we use them this year on the 20th May.
No. It is only good for that day. The date is printed clearly on the front and the rules stating such are printed on the back. The ones for this year look completely different too. I just kept mine for a nice souvenir!