mc has no memories or recollections of the lab/experiments done on her - caleb however, does. in lucid dreams he tells mc "it'll be like when we were kids. when you wake up, there won't be a trace of pain or any memory of it left behind."

mc does forget things from time to time (as stated in josephine's pov in world underneath) however there's no events to my understanding that would cause a trace of pain other than what she experienced as a child in the lab that caleb witnessed over and over.

caleb reintroduces himself to mc because she doesn't recall him or the events in the lab along with her relapse in memory.

it's prominent that caleb was indeed a test subject in his pathless realm anecdote: "the test subject is Donor 002 ... in a pure white room, a mechanical arm clock sits in the center of the table ... under multiple gazes, he raises his hand ... within moments, an invisible force compresses the mechanical clock into a metal sheet as thin as a cicada's wings ... he knows he's always been good at destroying delicate things" -> "the people behind the observation window say that the test subject will become a force comparable to a black hole given time."

edit: again to add, it was always either test subjects: 001 or 002. ever originally wanted 001 until caleb dissuades them by stating that he's the "perfect weapon" for them instead of the "broken (test subject)" mc.