It seems to me that Trent took what the Protestants cited as their beliefs, outlined the difference between the beliefs of the Catholic Church and said that whoever believed in other than what the Church proclaimed was excommunicated. It makes no judgement on the afterlife.
The way I have been taught is that Jesus is the head of the Church and we are the body (literally you can picture this as a human head and body) --- all Christians encompass the body. Some parts are further away from the "head" than are others --- but all are needed to make up the body.
I'm sure I'm not explaining this perfectly (I know I'm not), but maybe someone else can elaborate.