I've noticed a pattern where people will take this as their default assumption, and even selectively read evidence to the contrary in order to maintain that assumption.
For example, a while ago on HN[1], someone posted this link[2] about a CDC announcement titled "CDC director says data 'suggests that vaccinated people do not carry the virus'". The claim was that the CDC director, Walensky, insisted that vaccinated people do not carry COVID and insisted that they were 90% protected against infection, and the CDC wouldn't walk back on those claims.
However, when reading the article, it shows that the assumption that the CDC was using Exhibit A's method in their announcement was wrong, and the CDC actually used the more reasonable method in your Exhibit B:
> Walensky was referring to a new CDC study of nearly 4,000 front-line workers, some vaccinated and some not, who tested themselves weekly for COVID-19 infections between December and March.
> But more data is still necessary to say so definitively, which is why researchers are recruiting thousands of college students across the country to find out more about the likelihood of asymptomatic spread of this virus among vaccinated people.
[1] https://news.ycombinator.com/item?id=30649479
[2] https://www.businessinsider.com/cdc-director-data-vaccinated...