The problem is the difference between stating:
"masks have not been shown to be effective for the general population"
and something like:
"we do not know if masks are effective"
What was said was readily misinterpreted as "masks have ... been shown to [not] be effective for the general population", especially by a science-illiterate population reading with a non-individualist perspective. Whereas the second directly acknowledges the lack of understanding in an evolving situation.
It's preferable that we have the timeline in mind.
https://www.latimes.com/science/story/2021-07-27/timeline-cd...
One key aspect of the initial guidances regarding facial masks were based on the assumption that covid was not easily transmissible, which was proven to be false. Once that fact was acknowledged, the whole world pivoted towards widespread adoption of masks and lockdowns to hinder spread.
> It was definitely a black mark on the CDC response (...)
To be fair, the initial criticism towards mask adoption were based on what little they knew then. As the pandemic progressed and observations in somewhat controlled environments started to trickle in, the focus shifted to prevent a supply crunch that affected first responders. I recall that there was also a period where health officials admitted masks were effectice, but regular people would only wear them wrong thus they wouldn't work, which was also dropped.
What matters to keep in mind is that this adaptation took place in a timespan of a couple of weeks at these start of the pandemic. Thus, it's not possible to use this to justify any anti-mask and anti-prevention militancy.