It is highly uncertain if this party was ever held, but the fact that a party by the same group this year was dubbed The Ancient Party 2 1990, sort of suggests it was. It is not present on CSDB, though.

Promoted in TAT's june 1990 release of Atomix, thus "cu on the tat party in july", which also mentioned their upcoming demo Airdance III which carries a july release date. It is not a stretch to think that if the party was held, the demo was released there.