Umm… 
This is my understanding of the situation so far, I’m quite happy to be corrected here 
Since around 2017 (either .0400 or .0700 firmware on the OG Mavic Pro, I forget which) all DJI drones have been broadcasting DJI’s proprietary “beacon” that AeroScope can receive. Can’t think of a better word than beacon, trying not to use Remote ID in this instance. They added that capability to all their drones that were current at the time and running the same generation of firmware, so the Phantom 4 got it, the Inspire 2, but not the previous generation, eg Inspire 1, Phantom 3. Pretty much anything that worked with the GO4 app was broadcasting a “beacon” signal that AeroScope could receive.
That beacon contained things like the TOAL point, the current drone position, speed, altitude, direction, the model of the drone, the drone serial number, battery level, etc.
This was all long before the whole Remote ID thing of modern day.
That “beacon” was, and still is, proprietary to DJI. We’ll call it “Drone ID” here, rather than Remote ID. Detailed breakdown from a 2019 post: Anatomy of DJI Drone ID Implementation (re: AeroScope)
In more recent times, the requirement from FAA in particular (unsure of Japan’s airspace authority) is for all drones to broadcast a remote id signal which complies with the open standards.
This means you could retrospectively buy and fit a Remote ID module on an existing / old drone or fixed wing plane quite easily.
The remote id broadcasts less data, so no drone battery level and other smaller details, but still includes it’s own serial number (if you’ve retro-fitted one).
Today, all DJI drones are still broadcasting their specific fine details to any AeroScope with a 5km range and in recent firmware updates, as we’ve seen with the Avata, are also broadcasting the open remote id protocol in the relevant countries that require it. And that any Karen can pick that signal up with a suitable smartphone.
This is my understanding to date, quite happy to be informed otherwise and enlightened further if I’ve missed or misunderstood something here 