よくわかんないんですけど、指定席のチケットを取ってる時間の新幹線より早い列車でも自由席に乗れるんだったら、のぞみに乗れば青森行きの最終新幹線間に合ったんですよね。
それが可能なのか自信なかったし、イベント会場からギリギリでその新幹線に乗ったので、駅員さんに聞いてる余裕もありませんでしたけど(^^;)

I don't really understand it, but if I could've taken an open-seating regular train earlier than the bullet train on which I had a reserved-seat ticket, I could've made it in time for the last bullet train headed for Aomori if I'd taken the Nozomi.

I wasn't confident that would be possible, and I barely made it to that bullet train from the con venue, so I didn't have time to ask the station clerk. (^^;)