"It turns out that anyone can get a sample and they keep a database where they track that only so many chips across types are being acquired as samples by any one person (unless a rep is involved)."

Their website actually says that the limit is two parts for any particular device.

Not all devices are offered as samples, and it isn't necessarily clear when a device is not available for sampling.
I found this with one of the 1-Wire temperature sensors: I requested samples of 4 devices (via the website), but only 3 arrived. It was only when I enquired that they explained that the missing part wasn't available for sampling (didn't get a good answer to why the website offered it, though).