understand the word FULL
You are just giving your personal interpretation of "Full Nodes".
get a dictionary then
"not lacking or omitting anything; complete."
if a node is not storing the full blockchain. its not FULL
if a node is not fully verifying all of the data it receives its not FULL
if its not offering the full services available its not FULL
its common sense. stuff you can learn by actually understanding what FULL means in any scenario/product/service aka real life
Most vehicles have one fuel tank. If you fill that tank, it's FULL.
Some vehicle have two fuel tanks. If you fill both tanks, it's FULL.
The vehicle with two full tanks doesn't magically make the vehicle with one tank less full. Both are at the capacity they are designed to hold.
It's common sense, when you aren't trying to redefine what FULL means because you're a goddamn sociopath.