James. Do not be sorry for being analytical. That is what you need to be a good HI. I say bravo for thinking outside the box.
Off thread: In my younger days when I was not thinking as an adult but yet old enough to be well on the way to putting aside money and building a family, I would drive my friend that delivered sewing machines throughout the city of Montreal. The rag trade has a hug underground manufacturing sector. It still exists today. the rich like to keep themselves wrapped in the tax free environment ANY WAY THEY CAN!!! Look at the tags on top of the line manufactured clothing brands at The Bay, and other distributors of clothing. Tommy Hilfiger, Calvin Klein and the rest. Made in sweet shops owned by individuals that will surely go to hell by subjecting humans to suffering and a non living wage.
I have seen basements set up with sewing machines. true sweet shops. I know many an immigrants that worked sweet shops to become Canadian citizens and buy that home they would never get in their country.
There would be fresh air injected into the house for circulation at one side and exhausted stale air pumped out the other side. James you are onto something.
Bravo on the start to a solid hypotheses if you can add it all up together.
Electrical panels. 3 phase and you are onto something.
Single phase manipulated and you are onto something.
NOTE. That many vents become a suspect condition.
The neighbourhood will also be part of the detective story. Does the neighbourhood have a high ethnic population.
Walk or drive around the block/s looking for the same thing.
Great reasoning James. Bravo.
sorry for the edit.
We are there to observe and report. it not about why. it is about what we see. If it has negative consequences the wrie it up.