There were two crossovers last season that were intertwined between Chicago Fire, Chicago PD and Law & Order: SVU. Unfortunately for Global, they don't carry LAO: SVU - CTV2 does. IIRC, Global just had an announcement just before the 3rd and final episode in the crossover, at the start of Chicago PD, about events that occurred between Chicago Fire and the just-about-to-start PD took place on another show and they would join it "in progress".
As for a triple Chicago crossover event, Global will probably just shuffle their schedule for that one week when required.
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