Hi-(no flames please) I made a few double ADR last Sept. I haven't made any yet this year, but I might. I too, don't want to me left without a good dining place if our plans change. We have yet to use all the ADR we make-hey it's a vacation, plans change. However, that being said, I have always cancelled the non-used ADR as soon as I knew.
Since I wasn't sure if I could have two ADR for about the same time, last year I did put the extra 2 under my moms maiden name and made a note of it on my planning paperwork including the confirmation numbers. And I did cancel the ADRs when our plans changed.
Happy eating!