I think it's much more likely the Japanese variant is QS and not EV-4 - Warner-Pioneer Japan issued many domestic discs in QS (and SQ) in 1972 and 1973 before their US counterpart settled on CD-4 midway through 1973. More info on this in a discography/history thread I did
here.
Sansui (another Japanese company) was also aggressively courting labels, especially Japanese ones, to adopt QS as their format of choice - that's why you see Carole King's
Music come out in QS in Japan in 1971 before it was issued anywhere else. I think the same goes for Warner-Pioneer.
As far as the US LPs not being quad encoded at all, could this not be down to QS yielding a much greater front-rear separation? ...and I don't own a Surround Master so I'm speaking froma position of semi-ignorance, but does it even decode EV-4? I thought it decoded SQ and QS.