Perhaps in people who have been vaccinated, but not subsequently exposed.

I have no data to back it up, but I believe the virus is much wider spread than we know. With many vaccinated people having been subsequently exposed, perhaps multiple times.

This would serve to strengthen the antibodies.

I had covid in December. I was lucky to have mild symptoms. Then I was vaccinated. About a month after being vaccinated i spent 5 hours in a car with my oldest son who became symptomatic the next day. No way to know if he had delta, but I never had any symptoms after.

I isolated, but wasnt able to get a test.

Ive had another exposure since then that is less certain to have made its way into my body. Tested negative (at home test)

All anecdotal, but this is the chronology of pandemic to endemic.

Point being, my antibodies may have protected me. The vaccine likely did. But most likely is that they all are.