My understanding is that once a county court at law has found that it has jurisdiction over a case from a non court of record municipal court, a trial de novo ensues and there is no factual evaluation of what occured at the lower level of how the proper Judgment and Sentence came about, etc. In other words, once the county court of law takes jurisdiction, what occured at the lower level "disappears" and a trial de novo is to start. Am I missing anything?

You aren't missing anything. But consider this, since it is a trial de novo, should you dismiss at the county court level the offense goes away. There will be no record of the speeding ticket, littering, stop sign violation, etc. Something we learned (or maybe relearned) the hard way.