The last opportunity to study the effectiveness of mandating low-quality masks in preventing community spread during a pandemic was around a century old. (Literally, the Spanish Flu epidemic.) In the meantime a lot of new and untried modeling tools were in use, as well as updated disease models, and lots of reasons to question old data.
See https://www.albertahealthservices.ca/assets/info/ppih/if-ppi... for an idea of what was reasonable for educated specialists in public health to believe. Note phrases like, "There was agreement that although the evidence base is poor, the use of masks in the community is likely to be useful in reducing transmission from community based infected persons, particularly those with symptomatic illness."
So it is accurate to say that we had reason to believe that masks work. But it is easy to overstate how much we "knew" it to be true at the time.
The only reason masks were in doubt was the incompetent advice from WHO bureaucrats, and the bureaucrats on national advisory levels mindlessly droning it. This was not evidence based.
To get everyone to mask up, we needed to put the general public in low quality masks. And there was a whole heck of a lot less research on low quality masks being used by the general public.
But, regardless, I have no percentage in convincing you of what is true. Have a nice day.
