It says "low minimum 11T", which to me means they don't want you using a 10T or 9T smallest cog, and yes, these are both available. It does not mean you can't use a larger smallest cog so, 12T or 13T smallest cogs are fine. And you are correct, cassettes starting with anything but an 11T cog are increasingly hard to find and I also don't need or like them.