The Aria model likely does predate the Westone brand which didn't really kick in until about 1980. However, it could still have been a Mats build prior to the switch to the Aria Pro II label.
I suspect that the Session II was based on the Aria version in a reciprocal arrangement. According to some of Tom Presley's stories, there was a lot of shared (and swiped) innovations between APII and Westone during the brief period of Matsumoku's involvement.
p.s. There was no actual "law suit", that's an urban legend. It was a cease and desist order from Gibson to Hoshino concerning the open book head stock design. Other Japanese manufacturers took the hint and stopped as well.