The exceptions to the rule with the 3 line Pearl snare drums seems to be in the 6.5x14 size specifically and not with the 5x14 size regarding whether it is a brass shell vs steel shell. The vent hole on a 5x14 with 3 line snare can be either in the center or the lower position (toward the reso/snare side head) and still be brass, however, on a 6.5x14 3 line snare, the vent hole in the center is generally a steel drum whereas the vent hole in the lower position seems to be always a brass drum. I hope that helps.

That said, always do the magnet test!