Probably just go by the postmark? But I think it's silly to open yourself up to that sort of quibbling in the first place. If you are prepared to warrant the piece for the extended period, then do so from the outset and have done with it.
By the way, it still sounds very good. The only functional downside is I now do a lot more rate switching in Audio Midi. With the Duet, I just let iTunes upsample everything to 96kHz as I didn't feel I could hear any difference. With the Ayre, I definitely prefer CD playback at 44.1kHz. Will someone please write a native-sample-rate plugin for iTunes? Pretty please?