I just saw this thread
https://community.ricksteves.com/travel-forum/germany/if-you-miss-your-ic-train-because-of-a-late-regional-or-s-bahn-train
Just to set the context, it's about the first leg of a trip on a regional train but its late meaning you miss the IC connection. And the regional train is covered on the D-ticket. The thread is closed so I couldn't reply on top. But @Russ mentions
But you can prevent the problem. When you buy that non-flexible ticket, buy it NOT from your intended IC-train starting point, but from the station/stop on your regional train route that is located just prior to the IC-train starting point.
I've put my screenshots here which I will refer to below - https://imgur.com/a/F6VrmP6
In my example following @Russ's suggestion, I want to buy a ticket for Gapa to Würzburg. Screenshot #1 shows the ticket at 8:07 from Gapa. The station before the IC starting point is München-Pasing (arriving at 9:19 on RB6) as shown on screenshot #2.
When I query the new ticket between München-Pasing and Würzburg starting from 9:10am - screenshot #3 - the first train it gives me is München-Pasing at 9:28 - screenshot #4. This isn't the same regional train as the one I queried in my Gapa to Würzburg search - which should start at München-Pasing at 9:19.
So how would that work if a conductor comes and check my ticket?