To me, it's kind of insane that the whole "Intelligence Dampening Sphere" reveal was kept from us for so long.
Like, you'd think that GLaDOS would weaponize this knowledge sooner. But no, for the first part of the game, She remains surprisingly ignorant of Wheatley, and even once She does acknowledge him, it's very impersonal, compared to the vitriol She expresses afterwards. "Metal ball", really? That's it? As if She really coudn't distinguish him from any other robot in the facility.
...But okay. Seeing how good She is at suppressing traumatic memories, maybe it really took Her that long to remember; maybe there was something specific that needed to be triggered first. Whatever.
But Wheatley? Resident Mr. "Can't Keep A Secret To Save His Life"? You're saying that, after endless complaints about his jobs, he'd never mention his original occupation? That, after bringing up the human who managed to kill GLaDOS, he'd pass up the opportunity to boast about the kind of damage he was able to inflict on Her? That he wouldn't at least vent his frustrations if the whole ordeal was as distressing to him as it was to Her?
And yet he doesn't seem to be unaware of his nature, either. If he didn't know he was made to dampen Her intelligence, then, most likely, he'd just interpret the accusation of such as bluff and dismiss it. Instead, he goes into denial, yes — but barely shows any confusion and never tries to refute. Plus, compare the ensuing meltdown to how he reacts to being called an idiot during the pre-transfer struggle — it's not nearly as caustic.
And then there's... nothing else. No character elaborates on the topic further, as the game swiftly moves on to different mysteries. "Lab Rat" never brings up any specific core during Doug's flashbacks. Nothing in Portal 1 is recontextualized by this knowledge. And, of course, no new supplementary material on the topic was released since.
So far all that's left to do is to touch the scorched ground and wonder what the absolute hell went down between them.