I agree that it's not hard to tell the difference between the most common ones, but I understand people who are not confident about this, or haven't learned it yet.
Same about the "mixed drawer", with a bunch of feet without a name...
What is the risk of just trying? As long as it lines up with the hole, fits the rod, the rod operates normally, and it doesn't feel overly tight or loose...what can happen?
There is the width thing, of course - general rule is narrow foot for ss, wide for zz, usually the same as the width of the feed dogs. Also easy to tell the difference, but no damage done if you get it wrong, just suboptimal performance.
Always starting up real careful, a couple of cycles with the hand wheel to make sure there are no collisions between needle clamp and foot.