There are a lot of people who report they had covid but never had it confirmed via PCR test or serology.

This is a problem because data from this group purportedly about covid, such as "long covid" symptoms or the robustness of natural immunity, is seriously compromised.

You can see that idea here in this study and also in the difference between natural immunity studies which use self-reported data (which may indicate weak, declining or no protection), compared to studies which use PCR or serological confirmation. The studies in the latter group unanimously confirm the robustness and longevity of natural immunity.