Does it wash off (if so, probably sooty mold, nothing to worry about.) If not, how cold is it getting at night? Did the leaves recently fall off of trees that were making shade (and now it's sunburned?)

Does the leaf flesh appear necrotic in those areas, i.e., dead, dry, thin, or drained of fluid? Can you poke a hole in those dark areas easily with something like a dull pencil, or is the flesh as firm as the rest of the plant?

I think Tiffany might be on to something with her question about shade trees losing leaves. My Scindapsus pictus, a similar species to your "pothos," might be suffering from sunburn from that exact thing: trees just lost a bunch of leaves in a cold snap the last two days, and I hadn't realized how much sunlight was suddenly flooding in my window. If that's it, pothos will recover quickly. They're very resilient plants.

EDIT: the angle of the sun is much lower now than a month ago. Are you sure they aren't getting strong east or west sun that couldn't reach them a week ago? The sun comes about 20 feet into my apartment now, compared to less than half that distance a few weeks ago. I'm pretty far north, but sun angle can be tricky when the seasons change.

they don't appear to be dying where the spots are or drained. The spots feel normal except for the color. I'm 99% sure they don't get hit by sunlight there but I will double check tomorrow just to make sure.

Place a piece of clean, white paper below an affected leaf, then flick the leaf sharply with your index finger so anything on the leaf will fall on the paper. Then have a look at the paper with a magnifying glass. It doesn't seem as likely to me as sunburn, but the spotty pattern does look similar to thrips damage. They're TINY, so a hand lens is likely needed if your eyes are over about 20 years old. They're much easier to see against a white background. Mites also produce spotty damage. Some mites are visible to the naked eye, but I had an infestation of microscopic mites a while back that I never could see. Hopefully it's just sunburn on yours.

Well, I'm stumped. Definitely not getting any direct sunlight. And I did place a piece of paper underneath and shake it a bit but I didn't see any mites.

Is it in a hanging basket pot? Reading your initial post again, you said you were watering once or twice a week. That may be a bit much with the cooler temps if that was the regimen during the heat of summer.

Wow, it is puzzling.

It doesn't look like an ower-watering issue to me, but since we're not coming up with any more likely possibilities, then it is something to consider. This late in the year, it has likely stopped growing, even in Florida temperatures. Pothos tolerates drying out pretty well, so let the top couple of inches dry between waterings.

How long have they been in that soil? Did they grow well all summer? If so, they might be a bit pot bound now, which can cause some dry spots in the soil, or some roots to become so restricted that they aren't able to draw enough water. It isn't the best time of year to re-pot, especially if something else is causing the problem, but you should at least check this.

Can you pull the entire plant out of the pot with the soil and rootball intact? If so, a photo would help us. Check the root ball and medium for dry or mushy spots, for discolored or necrotic roots, for root parasites, crowding, etc. A few, small disrupted places in the root ball where you dig in to check the condition won't hurt it, even this time of year, and if it's very pot-bound, you can plop the entire thing into a larger pot of soil until the spring when you can do a better job or repotting, detangling, root-trimming, and so on.

What parts of the plant are affected the most? Were the oldest/lowest leaves on each stem affected first/worst/most, or is the damage worse on the younger, more tender leaves? Are there any parts of the plants that aren't affected? When was it last fertilized, with what, and how often? (Do not fertilize it now- that's the worst thing one can do to a sick plant if the illness isn't due to fertilizer nutrient deficiency.)

It might just be lighting, but the plant in the upper photo appears to have an overall yellowish pallor. That would support Tiffany's hypothesis of too much water. Also, I see a yellow leaf near the base of a stem in the second photo near that little sprig of Acacia or whatever it is that's taken root there. Some yellowing is normal, but check through the lower leaves for more yellowing. Too much water or nitrogen deficiency both tend to affect older/lower leaves first. Evenly yellowing lower leaves is more indicative of too much water or poor drainage, while yellowing that begins at the leaf margins is more often nitrogen deficiency. Other things can cause yellowing though, and that curious staining appearance isn't typical of either issue, so don't fertilize at this point.

More photos wouldn't hurt:

Entire plant

Root ball free from the pot

Close-ups of the "stains"