Hi Dave, welcome!
This almost seemed like clairvoyance. I would see someone and just "get" something in a way. This knowledge always seemed profound and absolutely true but mundane, as if how I came to know this was the most natural thing in the world.
More important than this is the knowledge that this knowledge is subject to the 3 characteristics, seeing clearly leads to "unbinding" or "disembedding" from these phenomena. No longer thinking it is "you" and thus the sense of profundity/absolute truth/mundaneness/easefulness/clairvoyance is impermanent (comes and goes) and not worth investing in self or I. How is the knowledge "known"? Rather than focusing on the specifics of the knowledge itself. Since this is in the past, focus on how the memory or mental phenomena of it is known...
Sometimes knowledge can seem "absolutely true" in one moment, but thinking back on it makes it seem ludicrous or "absolutely false" or "what the hell was I thinking?" This is particularly the case where a sense of "psychic powers" may have been involved, since you mentioned clairvoyance. This makes a lot of the psychic powers, altered states, and extraordinary experiences something "unreliable" or perhaps more accurately, delusion and suffering. Delusion being more focused on phenomena that causes suffering rather than focusing on its truth value, which can vary from moment to moment (or at least the sense of its truth can vary).
Once I was driving on icy roads when a chaotic car accident erupted around me. I found I could instantly turn off unhelpful emotions and focus single-mindedly on navigating the chaos. My main question: Do you think these things were early insight-wisdom or something stemming from strong concentration practice, or both? I would love to cultivate these abilities again. They were very helpful.
Yes, these were likely from both insight wisdom and concentration practice. Though perhaps more from concentration. Either way, this event was in the past and is not now. Whatever the "cause" of it is far less important than the specifics of what's going on now. The ability to have super-human reflexes is impermanent, and does not grow in direct proportion (linearly) with spiritual progress and may have had more to do with the specifics of that day and time and place than anything in the months preceding it.
So, question two: Does this mean I've been a dark-night yogi for half my life?
Dark-night yogi is a self-proclaimed label. It is entirely possible that you have been oscillating among the early stages these past 16 years, mind and body, cause and effect, A&P, but it is also entirely possible for this to happen and for it to go unnoticed. More important is what do you think? if your gut is that you have been experiencing pervasive disgust, misery, frustration, possibly depression for a good portion of the time, then probably yes. If not, then no. If yes, then that is all the more incentive to start up a practice again.
The fact that you are here and posting about this suggests the somewhat involuntary impulse to make progress. Usually manifesting as a sense of incompleteness, wanting to find something or get something done that is unfinished. For me, this is present, but can increase in intensity at certain times without obvious stimulus.