As to the lower than expected seroprevalence results, the correct interpretation is not that reality is wrong and our original hypotheses are still valid (as many seem to believe).
What is causing lower than expected seroprevalence? Various concepts have been put forward and are being studied: pre-existing immunity; T cells; variation in susceptibility; perhaps something else.
We do not need to know the exact inner workings of the mechanism(s) in order to reach meaningful conclusions and make progress.
...end.