In 2008, I had one of the advance purchase, train specific (at that time called Dauer-Spezial) tickets from Walkenried, a small town south of the Harz, to Karlsruhe. The first leg was a regional train to where I would catch an IC to Karlsruhe. For some unknown reason, the regional train sat for half an hour in one of the small stations on the way to the IC, causing me to miss it. I went to the ticket counter at the station and showed the clerk my Dauer-Spezial ticket. He looked up the regional train on his computer and saw that it had, indeed, been delayed. He wrote the number of the next long-distance train to Karlsruhe, an ICE, on my ticket, and I took that train.
He did this in accordance with the AGB, which says that if you miss a specific train because of a fault of the Bahn, they will put you on the next available train. So, I am quite sure that if you go to the station in Nürnberg and present your ticket, they will accommodate you. The only problem I foresee is that, I believe, first class tickets come with seat reservation, and Nürnberg to Berlin might be a busy line with full trains. You might not be able, at a late date, to get a seat on the train you want. Are you registered with the Bahn? If so, you might be able to go on their website now to rectify the problem. If not, I think there is still an email address, to which you can write, shown on their website.
