When looking for a chainring, I see that Shimano specifies whether it is for 2x or 3x. I'm guessing that the pins (protruding rivets) on the former will be on one side only, and on both sides on the latter.
They're also labeled "PCD", but the numbers suggest that it is an alternative way for saying BCD.
Then they specify whether it is meant for 11s, 10s, 9s, 8s, or 8s/7s. I'm guessing that the thickness of the chainring exactly matches the exposed width of the pin between the inner plates. In other words, it would be possible to use, for example, a 10s chainring with a 9s chain, but the chain would wiggle slightly side-to-side. It would not be possible to use a 10s chainring with an 11s chain, because the chain would not sit properly. It would remain "elevated" at a larger radius (until eventually eating into the chainring to sit properly).
This all makes more or less sense. The puzzle is that some noname brands indicate "Machined Alloy Fits 7 to 12 Speed".
Why will some chainrings fit 7s-12s while others are meant for just, say, 10s?
Context of the question: I'm trying to drop my larger chainring from 50t to 48t or even 46t. I'm partial to faster rpms, and at 90rpm a 50t will let me approach 50kph, and that's simply not useful as I'm not racing.