I also live in 9b about 40miles, inland. I really don't know what causes these problems, at first I thought that I got water on the leaves and they then got too cold. Some plants get them and others right next to them do not. In the winter if a section of a leaf gets too cold, it will show up months later getting brown like a paper bag. Not enough water during winter will also cause this and too much will rot the leaves. I water by hand each plant trying not to get water on the leaves Winter or Summer.
I have small spots as well, I still don't know what causes the problem. Other people who break all the growing rules with Sansevieria don't have these problems, and the Sansevieria that I grow out side also don't seem to have these problems, yet I have seen this happen to 100 flats in a covered green house with no temp. control go down over Winter. I haven't figured it out yet, if you do please inform the group. It could be poor circulation or drafts that may cause this problem, I heat my green house, so it can't be that, unless I keep it too hot, but the plants closest to the heater don't have the problem. I don't have any diseases in the greenhouse, and so far have not seen anything chewing on them. Most all of mine have flowerd this past Winter season, now they are really growing. Please keep me informed I really would appreciate your input. Norma

Ah, so it is a bit of a mystery then!
This one is sitting in pot in my bedroom. About 2 feet away from the window, so indirect sun in the morning, and that's it. I don't water it much. Usually, I only water it the leftover in my watering can, or the leftover from bottom-watering my haworthia for 20 minutes.

I don't heat my place in winter, cuz I'm cheap. It probably got down to about 4 or 5 some nights in that room. Humidity relatively high though.

In addition to the random brown spots (of which that one in the picture is the worst), during the winter two leaves got brown and sticky (one at the soil line, one about two-thirds of the way to the tip), and flopped over. I cut them with my shears and tossed them. What's weird is that the one that was sticky and weak at the soil line, i thought "well, I'll just pull this one out", was attached to a younger shoot that was (1) totally healthy and (2) had different markings. I chopped its... what is it with Sans, a rhizome? Anyway, I cut the bit under the soil where they are attached in half, discarded the rotting bit, and replanted the healthy half where it had been, and it's fine now.