Seems they have been messing around with it a lot longer than first assumed as you can see below. The screenshot is from a 10 page write up presented in a paper from
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/77BBFFC8CDBB77DAEDB4BEBCA3D0F14F/S0022172400022294a.pdf/div-class-title-coronavirus-antibody-titres-in-sera-of-healthy-adults-and-experimentally-infected-volunteers-div.pdf