I’m just guessing, as I’m not familiar with the system, that all it does is make “pink strips” available to the controllers along the intended routing at +\- “x” minutes from the notified times, with aircraft callsign and aircraft type already on the strip? So when an aircraft calls out of the blue the controller can scan the pink strips and select the appropriate one?
(Similar to traditional IFR strips - which appear x minutes before they are due, except that a squawk won’t yet have been allocated?)