They're probably all LG panels under the hood[1]. Different resellers have different pixel policies, and they can be a bit hard to keep track of.

On these size screens, Apple won't replace <11 dark (dead-looking) or <9 light (stuck-looking) pixels. HP's policy is about half that. Lenovo is like 4 or something. Some of the other manufacturers have even more complex policies which depend on the position of the stuck/dead pixel.

And in practice, if you complain well enough in the store, Apple may replace for you even if you're under the line.

[1] When I say "they", I mean these 27" IPS panels, whether they're from Apple, Dell, HP, or some random Korean company.