Perhaps in training matches (no one wins all the time) or in war - he was on the losing side in at least one battle.
However, in 60 duels, he never lost.
Indeed. That shows great courage and skill. However that wasn't Aikido. Secondly you could say from a spiritual perspective every win was a lose. Thirdly there was a certain charachter in the book who was sent out to capture him a few times, without fail I might add. Funny how no one talks about him.....