That is exactly what they did, although I'd use a word a bit more respectful that "game." They knew shed ET insulation occurs, had measured its extent on numerous occasions, and were actively engaged in reducing or eliminating it (reduction via sanding hard outer layer of ET insulation off, in certain areas of ET, elimination by understanding mechanism that causes ET insulation to shed). NASA (I think) honestly believed, based on experience, that any damage due to ET insulation shed was only a matter of turnaround, and not any risk to mission integrity. They also reviewed information relating to this specific flight.