It looks like the proposed Covid-19 antibody find for Italy from 2019 is not uncontested among the science community, here is a comment from virologist Marion Koopmans [1], who was trying to validate the study's results:

"Yrs, we tried. Sofar have not been able to confirm. Serology in low prevalence situations is challenging so our criteria are stringent ( triple antigen positive and neutralisation). With that no positives pre march 2020 in our country and sofar not in panel from italy"

[1] https://twitter.com/MarionKoopmans/status/141665264260494541...