Didn't USC or another CA school do a similar study and found that the number at the time could be up to 50x(which is way to high even in my opinion!) more people then knew they had it.The Penn State College of Health and Human Development did one such study throughout 2020 and into 2021 but I've never seen results published. My daughter was a participant in the study and she received a $20 Giant gift card each of the times (2) that she had blood drawn. The first time was May 2020 and it showed that she had had a previous infection, which she didn't know about as she hadn't had any symptoms.
There was a French study to looking at long covid that had 60% of the participants who didn't think they had covid actually did. I'm posting this for that stat not the long covid part.
A huge French study shows BELIEVING you had Covid is associated with many later symptoms. But ACTUALLY having had Covid isn't associated with any (except loss of sense of smell).