It makes me wonder

I met a lovely lady at the Sewing for Pleasure Show in Birmingham last March who ordered a pattern that I had sold out of. So I posted it out straight away after I had it back in stock. Just after I'd sent it she phoned to say she had given me the wrong house number and feared that it wouldn't arrive. So I sent it again to the correct address and she then very kindly let me know after it had arrived.
By that time I thought if the other one couldn't be delivered it would come back to me. It didn't, and to be honest over the time I completely I forgot about it. Lost in post. Until today - an envelope arrived with a Royal Mail note saying "not known at this address". At first I coulnd't really make anything of it as the name and address didn't ring a bell but when I opened it and saw the date it was posted it came back to me. It was sent on the 5.4.13!
Now, Royal Mail, can you tell me where it has been for the past 9 months?