The description appears to be something more similar to the "reduced-carrier single-sideband." There's long history behind the variants of sideband modulation:

https://en.wikipedia.org/wiki/Single-sideband_modulation

In the same article, vestigal sideband is reported as used around that time for modems:

https://en.wikipedia.org/wiki/Single-sideband_modulation#Ves...