Finally a question to an interest of mine: local history of Württemberg.
First, before Bismarck, births/baptisms, marriages and deaths were only recorded in either Catholic or Protestant Church books. They are generally available up to the Thirty years Wars barring local incidents. Now second: the specific situation in the early 1800s in the kingdom of Württemberg. In short, the Württembergian duke of the time supported Napoleon, was rewarded with a recognition as King of Württemberg and with a massive gain in lands in the South. Those lands were taken both from the Catholic abbeys as well as local Catholic peers which controlled what is now South Württemberg and were fighting for the Austrian Emporer against Napoleon. Especially the various abbeys were immensely rich with vast holdings and treasures. The king took gold and art and gave land and buildings to his cronies in addition with a better title. Upheaval followed and books got lost. The whole process is called Secularization and is an own area of research. Now to the dead end in your research. As local history in Württemberg is very fractured both though rule and denomination, your dead end can be