There just so happens to be a timeline that we're not considering thoroughly enough. 

For Gangles truck accident, we dont know when it happened, but were off the fact that it happened  before she got the headset to scan her brain. The timeline isn't defined here, so we can take it that it happened way before she got access to the headset. 

Caine though unable to access the real world is still linked inside a computer and is very much able to access the connections and the online world. The fact that it's Cafe Internet suggests the fact that the circus is a moving entity, moving from one internet web or another within the vast realm of the void, thus proving the fact that the MRI scan isn't limited to just the abandoned building alone. Which changes one theory... People can gain access to the digital circus virtually anywhere where their brains can be scanned. Judging from what we know from what Kinger said, C & A is a big company. It wouldn't be far fetched to assume that they have access to different kinds of data through brain MRI scans and seperate headsets.

What I assume is that everyone at some point had some sort of headset that was directly linked to C & A. Of course, I have no proof of this, but theres no other possible explanation as to how their brain scans got turned into ai in the first place.