Which ones are you thinking about precisely please? If the sim card is out of order/removed and if there is no connectable wifi network where you are I don't understand how a smartphone could leak a seed outside neither any data.
Even without a SIM card and on flight mode, phones ping for cell towers, search for WiFi networks, can send and receive Bluetooth/NFC/RFID data, and more. The NSA have said they can still track phones even when they are in flight mode:
https://threatpost.com/nsa-warns-smartphones-leak-location-data/. The average person also cannot verify a single thing that flight mode does. Simply turning it on and believing that your phone is now airgapped is a fallacy.
You can use devices as cold wallet without having to sacrifice them, that was my point.
If you are no longer using them as a cold wallet and have emptied all the wallets they were storing, then sure, you could put the WiFi card back in and connect it up to the internet again. You would have to start from scratch again in terms of airgapping and formatting the device if you wanted to use it as a cold wallet again though. You can't just reconnect and disconnect on a whim and think your device is still safe.