Mailed the supplier to ask, they said "Oops" and sent a pair of new ones... Then both pairs arrived. Not sure in which order, but anyway the first-sent ones had apparently got stuck somewhere in Finnish Posti and/or Customs. Phoned the supplier to ask if they wanted one pair back, was told not to bother.

So, sorry Rand... That little anecdote yields no useful advice either way; doing what I did might or might not have the same result I got. All told, probably what others have said: Don't nail them up anywhere for a while yet, in case they get in touch and want them back within the next month or whatever period you find appropriate. After that, they're yours.