My last question is a bit different. What if there is a huge number of these watermarked light sources deployed, such as in consumer products, each with a unique code that could be verified against... can you identify which one/few of those millions/billions of devices were present?

(Once you have an identifying code, you can go through supply chain and sales information, and through analysis of other videos, to likely determine location and/or owner/user/affiliate.)

Nope. They used a fake vaccination drive to obtain DNA samples [1], which led to serious distrust in anything "public health" even up until Covid [2].

[1] https://en.wikipedia.org/wiki/CIA_fake_vaccination_campaign_...

[2] https://www.npr.org/2021/09/06/1034631928/the-cias-hunt-for-...