Tiller wouldn't have been given a bull of excommunication by surprise. He would have been confronted first in private, then in the presence of a few witnesses, then maybe in the parish council (not always the last one).
In other words, he had to have been pretty flagrant to get excommunicated.
Interesting...so excommunication is handled at the parish level in the LCMS? If so, is it binding on any parish in the synod?
You are almost certainly right. Excommunication is a last step, after previous futile admonition.