Agreed - will try to find out more from my mom (just had a brief chat with her), but it looks like if you want point-to-point wheelchair assistance from the arrival gate in T3 to the departure gate or lounge in T5, the wheelchair person will provide the assistance but only via the landside inter-terminal shuttle bus, requiring clearance of security in T5, rather than providing it via the airside TTB which doesn't require the passenger to clear security.