Taking a different RE train
 

I'm on a short (40 minute) ride on RE train to get to my ICE connection. I know I have to take the ICE train I'm reserved on, but do I have to take the RE train that's shown on my ticket?

There are no seat reservations on RE trains, and no reason why you can't take an earlier or later one. Conductors are looking to see if you have a valid ticket to your location. Don't try this on the ICE trains if you are booked on a specific one unless your ticket is flexible. There is a good chance you'll not even have your ticket checked on the short RE ride.

RE trains on a discounted ticket are not "train specific" so-to-speak. HOWEVER... make sure you are going on the same routing as the one printed on your ticket (i.e. if your printed RE train itinerary is the most direct routing, you cannot take a round-about RE train itinerary instead).

No problem to take any RE (or S or whatever is available as commuter trains) to the point of departure of your ICE train (as long as the relevant route in on your ticket). The same applies for any connection you have after arrival of your ICE train.

New twist... is it ok to take RE train a day earlier than one that's shown on the ticket?

>New twist... is it ok to take RE train a day earlier than one that's shown on the ticket?

No it isn't. Your ticket is only valid on the date/during the period that is printed on it.

Sure? I remember something like "NV/max. 2 Tage vor/nach festgelegten Zügen" or is that only applicable to the return journey?