Sailing is correct.

When ASA was bought it had its own code and use to award PS ASA travel to its employees. Delta bought that code when they bought ASA. Delta kept that code when they sold ASA, but the vestiges of ASA's old code and pass policy remained. SkyWest just did a "me too" since management gives them anything ALPA has to keep the "student council" in "power" and avoid a real collective bargaining agent on the SKYW property.