The problem is keeping up, for me as well.
Kangers aren't labeled so I can't help with those, the CE5 and the Vision stone innards same thing.
The Universals have images that correspond to which one they are on the website and have measurements pictures with the caliper in the pic showing the size, you can determine it that way if you have a caliper. Also you can determine it by comparing the size, 2mm is not a lot, but up against each other it should be fairly easy to tell, also one has one fat and one skinny wick and the other has 4 wicks.
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I do not know what the original Nova took because I didn't carry it, but I do know all the new heads I have fit what I carry (except for the mini) and the 2.5, there is a little leeway in the newer Vivi so it makes it easier.
The picture of the Vivi Nova is a generic picture from Vision, I haven't taken an updated picture. I realize this is a bad thing, I know I need to change it, sorry

same for listing compatibility, they do not fit the older one (based on what you've said) so I need to update that as well.
As soon as I am out of this run of the universal I think I am going back to labeling them only for what they are used for exclusively because this is getting confusing and I'm not making it any better. I was trying to help by getting heads that would fit most items, it started out with the Thor and the Vision because they are the exact same item and the heads also fit the Vivi Nova and the new CE5 (not mine) but it seems like it just made it worse
I've already made my next order and only ordered ONE type of head coil to make it a bit easier and when they come in I will again make sure they fit everything it's listed for.
I'll see what I can do about making some sort of chart.