Does this refer to DevAdr, and then specifically for "Activation by Personalization"?
The DevAddr consists of 32 bits identifies the end-device within the current network. [...] The most significant 7 bits are used as network identifier (NwkID) to separate addresses of territorially overlapping networks of different network operators and to remedy roaming issues. The least significant 25 bits, the network address (NwkAddr) of the end-device, can be arbitrarily assigned by the network manager.
For Over the Air Activation, this DevAddr is only known after activation, but then a DevEUI is already known, which is truly unique and not related to any gateway location:
6.2 Over-the-Air Activation
[...] The join procedure requires the end-device to be personalized with the following information before its starts the join procedure: a globally unique end-device identifier (DevEUI), the application identifier (AppEUI), and an AES-128 key (AppKey). [...]
6.2.1 End-device identifier (DevEUI)
The DevEUI is a global end-device ID in IEEE EUI64 address space that uniquely identifies the end-device.
But one could also hard-code the DevAdr in the node:
6.3 Activation by Personalization
[...] Activating an end-device by personalization means that the DevAddr and the two session keys NwkSKey and AppSKey are directly stored into the end-device instead of the DevEUI, AppEUI and the AppKey. The end-device is equipped with the required information for participating in a specific LoRa network when started.
I guess Activation by Personalization is impossible with TTN being global: the NwkID only being 7 bits, TTN won't have its own unique NwkID (but probably needs to know what identifiers are already used around a specific gateway)?