I can reliably reach 6th jhana, but am not too sure about 7th. A few times during meditation, I had an experience that was visually like watching an old CRT TV turn off, where all visual content collapsed into a line and went away, leaving pitch black. Was that it? How would you identify 7th jhana?

Some time back I had recorded a series of talks with my friends on discord. These are 4 talks covering prerequisites, access concentration, jhanas 1-4, jhanas 5-8.

Talk number four covers the discussion on jhanas 5-8. Its basically me and other experienced jhana practitioners along with a few people aspiring to learn the jhanas having a structured chat. Check out the audio file on this folder on google drive. Maybe you will find it helpful.

https://drive.google.com/drive/u/1/folders/1rtLrOyfiHzq_Ed0Go2B_zqxExa-Q49IJ

For me, the sixth jhana is already essentially devoid of visual objects, but the seventh jhana is devoid of all objects. It is the realm of "no-thing." So there is no thing that can be oriented toward, no sound, or sight, or touch, or thought. 

The way it usually progresses for me is that fifth expands around me and there is a strong sense of expansion into distance, then in sixth the sense of distance ceases and there is a homogeneous field of consciousness which is centered on me, the perciever. Then in seventh, the field drops away and there is nothing left, and yet the awareness of the nothingness persists, without being specially located at the center. 

I tried it this morning and may have gotten it, and it seems somewhat consistent with both of your descriptions. In 5th, the sense of boundary between me and the universe disappears and there's a perception of infinite space. In 6th, the sense of distance is replaced with a homogenous field of conscousness exactly as described. Then after focusing on the lack of inherent existence of all perceptions, I get the same 'gear shift' feeling that I get with any other jhana and that sense of infinite consiousness drops away and leaves a sense of there just being a void with nothing in it.
However the eyes and ears are still operational so there's still some perception, but it's all faint and feels 'out of reach' for lack of a better word. I guess that would be a light 7th jhana? My earlier experiences of things going to pitch black cause some confusion because this certainly wasn't as deep as that. Maybe that was a stronger 7th or possibly an 8th, since visual perception went away?

Yes, that's a good description of the seventh jhana. Please let us know when you access the eighth. A good description of that one would be a great read.

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My personal "jhana" experience is a bit strange and rather inconsistent.

There are "whole jhana" experiences, those occupy a great deal of consciousness, and there's "tiny-jhana" experiences.

For example, I can have a "nirodha samapatti"-like experience, but only for a single object. I've tried that mostly with a table tennis ball. So, it can literally fade out of that reality, as a whole, in an instant, stay gone for a few seconds, and fade back in. In the meantime, environment adjusts. For now, that's mostly a perceptual thing. I've never tried touching it while it's gone, but moving the eyes too much makes it reappear.

When the room is dark, most things are dark, and dark objects can disappear more easily, until you get used to them.

Maybe it can happen to you when you are just waking up. There's few boundaries, maybe no boundaries, and things just look black.

Everything is vibrating, to some extent. Sometimes more and sometimes less. It's like perception updating itself.
Sometimes there can be different "overlays", like layers. Imagine seeing the wall and you can mentally paint on it.

There are some states, like... "pure black". Just a while ago I've had an experience of bright light flashing rapidly. It happened over and over and over, over multiple days. That light was similar to the other state. Oftentimes, for me, there is an immediate jump from "normal" perception, or "stable" perception to "white-like" perception. It's difficult to describe, but it's like white or very subtly yellow, reminds me of lightning for some reason, but that might just be a weird subconscious association. Then follow disappearing and reappearing.

These "overlays" don't feel like overlays most of the time. Or at least they didn't, before it integrated into "baseline" experience.
Sometimes there is a black/grey overlay, especially when moving from existing to disappearing. It feels as if there are 2 balls or 2 circles or 2 fingers or whatever. One which is "real" and another which is like the opposite? like an anti-image, perhaps. Maybe that is how things become thoughts. And when they match and stay like that for a while, both fade and environment tries to look rather normal again. There can be different "fixes" like moving from one "main-eye" to the other eye, to change the perspective. Eventually it all resolves itself. Perhaps this is vision repairing itself.

There can be other overlays, like purple overlays or thought-overlays. If I look at the wall for 30 seconds or so, there can appear a purple circle. These are thoughts, I guess. Sometimes it can be (strong) red, green, or blue. There can also be a different kind of overlay. Either a certain area becomes darker, or brighter. If I look at my black mouse for 3-5 seconds and then at my table, there will be a different color on the desk, in the form of my mouse.

Sometimes, especially in movies, there can be another form of that. People's eyes can disappear, they can look black, or they can have this lightning-feeling. These seem to me like concentration states related to tiny details.

Similar experiences can happen with the whole field of vision, regardless of whether eyes are closed or open. When the eyes are open, it would usually have to be dark though, or at night, or it would be the balancing of a stronger concentration episode.

Anyway, I think i've only experienced 6th Jhana once and 5th Jhana twice. Sometimes my baseline feels like a hard-jhana, and that would make sense with the naturally occuring psychic power experiences.

Jhana 5 was mostly a physical/body experience. 6th mostly a head experience. and 7th/8th/9th mostly a visual experience. (black, lightning, disappearing). If you were to experience 7 to 9 with other senses, I can imagine that you'd have details fading. For example, why is it black? Maybe because there is no real experience, pure thought (purple) or are some areas disabled? Why is there this lightning? Perhaps because there is perception and thought at once? or maybe there is neither? Maybe there is a "conflict" between being and not being? And, for the last, perhaps all of that is just disabled, the whole area. So, you might have the absence of a body for a while. Maybe you couldn't tell whether there is a body or no body for a few moments.

Perhaps I'll be able to provide a better answer in a few months. I'm also curious about the bodily experience of upper jhanas.