They are not “variants” & not rare. I know you didn't ask this but I keep seeing the term “rare” (& others) abused so often by sellers, I just wish to clear that up. It was the way they were cut / produced. With 150M produced it is likely that stacks/bundles (x100) or bricks (x1000) of them remained as they've been available for at least 10 years for $10-$15 each (UNC).
Banknotes produced before 1900 (& even later) were cut by hand. They are not “errors” either so be wary of what sellers claim (sheets may have also remained). Usually, these are difficult to find well-centred (which would be the one to buy). Good luck!