When G and H shells are used in reboilers (with boiling on the shell side) the longitudinal baffle may be perforated. Its purpose is to help distribute the boiling stream along the length of the exchanger. The seal problem which was noted for F shells is therefore not important.
J shells will have normal segmental baffles as in E shells.
X shells may often have a few inlet and outlet nozzles to help distribute the flow over the length.