Partly welded exhaust has been common on American cars since the 70's. Depending on how the car was assembled, at least the tail pipe was welded to the muffler and sometimes the pipe just ahead of the muffler too. When any part of this welded assembly needed replaced, it was usually a replace all 3 parts. Sometimes a pipe could be cut and muffler installed. The factory prewelded system eliminated the need to adjust pipes to fit and is much faster to install.

As for what to do now, If the joint needs to come apart to take suspension apart don't weld.