joining my train one stop later

No problem. If you purchased seat reservations, they expire after 15 minutes, but because EC 173 departs Berlin Hbf at 8:59, and Berlin Suedkreuz at 9:05, your seat reservations will still be active. The conductors will not even start checking tickets until after you depart Suedkreuz.

I won't tell!

Usually the ticket checkers are on the trains, not at entrances to platforms or rail cars. So I can't imagine how they would even know. Unless there is a "hidden city" rule - and crackdown - like I've been reading with airlines.

Usually the ticket checkers are on the trains, not at entrances to platforms or rail cars. So I can't imagine how they would even know. Unless there is a "hidden city" rule - and crackdown - like I've been reading with airlines.

There isn't. Most likely, the ticket will be issued from "Berlin" (which covers all train stations in the city, including S-Bahn--but not U-Bahn or tram stations) anyway.

Great that you're taking the EC train to Dresden. I would too. It goes direct. After Dresden it ends up in Prague as the terminus.

If you take the ICE Berlin Hbf to Dresden Hbf, you need to transfer in Leipzig Hbf, which is all right, it's a huge Hbf. I prefer going direct.

To allay any concerns, just get to Berlin Hbf to take the direct EC to Dresden. I found Berlin Gesundbrunnen station a bit more taxing

You can actually get on the train at any station along the route, and it wouldn't matter in the least (excepting sleepers, possibly, but there are hardly any of those around any more).

If I had a ticket from Hamburg to Munich for instance and got on the train in Nuremberg only, nobody would care. They only want to know if I have a valid ticket for the train I am on. Why should they care if I paid for more than I am actually using?

The only thing that this would affect, as Sam points out, are your seat reservations. Those would definitely have expired by the time I got on the train in Nuremberg. :-)

No problem.