I think we more specifically know something emerged that was much more deadly and contagious around January/February. That does not completely eliminate the possibility that an earlier variant was present, which might be cross-reactive and might provide antibodies for some. We’ve seen that happen multiple times since then. Knowing if a lab leak was likely could help clarify this perhaps, since those may be opposing origin stories.
You can see where it compares infections to proportion of strain that they only spiked when "L" disappeared and one or more of the "G" ones became dominant. There's only 7 countries listed here, but I think I remember a different article that had more, and the pattern was pretty consistent.
There have been many variants that emerged in the US[0][1], but none of them have been significantly more infectious than the original Wuhan variant (until the Epsilon variants emerged very recently). Most of the ones that are more infectious than the Wuhan variant got nuked by even more infectious variants from elsewhere. I think perhaps the impression that there haven't been any variants stems from the fact that none of the big variants of concern have been from the US, which appears to have just been luck.
