I haven't read the court documents, but this seems theoretically solvable by just only accessing the backdoor on any particular phone once you've seen it send a

I haven't read the court documents, but this seems theoretically solvable by just only accessing the backdoor on any particular phone once you've seen it send an incriminating message to a phone you are already accessing (and getting judges to sign off on warrants for it, paperwork is probably a nightmare). You start with the head honchos phone, someone texts him about a drug shipment, so you get a warrant to access the backdoor on that phone as well, and so on. As long as there aren't isolated cells, you get every cell phone. Since you're relying on the head honcho to push the phones, there probably aren't isolated cells.