GE described its 6FG5 and 6FS5 as being of the “shadow-grid beam pentode” type:
These valves did not have a suppressor grid; what was shown as a fourth grid on the pinout diagram was actually the set of beam confining plates.
GE’s nomenclature seems reasonable in the context that it used the term “beam pentode” for valves such as the 6AQ5 which were more conventionally know as beam tetrodes. So, the term “shadow-grid beam pentode” referred to a beam pentode to which a shadow-grid had been added.
On the other hand, RCA referred to its 6GU5 as being a “beam hexode”:
It typically used the term “beam power amplifier” for beam tetrodes, but then showed these as having a grid #3, even though they had beam-confining plates rather than a suppressor grid. Whether the 6GU5 had, for grid #4, an actual suppressor grid or beam-confining plates is not unequivocally deduced from the available evidence.
Cheers,