I have a quick question, can anyone help, if you know the answer?

I received a voucher for a return flight HUY-ORD which changed so often that the eventual itinerary was a day earlier departing and the return via a different route, so I managed to get a refund voucher with the extra 15% value, which fell well, as I now wouldn't be making the journey anyway.

I would like to do the journey at the same time next year, though, but I'm conscious that my voucher is worth more than the original cost.

Do I have to spend the whole value of the voucher on a single itinerary, or will I be able to spend the voucher on more than one? For instance, I could maybe get a TATL flight more cheaply on DL or VS from LHR, and have a bit of money left over on the voucher value to go towards a weekend trip to AMS.

Or do I have to spend the voucher all in one go, in which case I'll look at upgrading my flight somehow?