> Another aspect of older people (and again: Parkinsons and Alzheimers in particular) is a loss of the sense of smell. Which may mean that odors otherwise noticeable and addressed aren't.

I highly suspect you hit the nail on the head here from personal experience: My grandma no longer has any sense of smell (or taste, actually) at all. I recall at one point discovering a particularly pungent smell was caused actually by a cleaning solution, I think it was like an old can of Lysol that had no substance designed to improve it's scent, that of course, she wasn't aware smelled worse than death.

My biggest fear was things such as her potentially not noticing a natural gas leak, because the default indicator depends on a sense of smell. (I found out you can buy "explosive gas detectors", which are different than carbon monoxide detectors, if you want an audible alert for this.)