Just more or less random thoughts on the subject, mostly the issue of why would non-Christians have positive near-death experiences, why they might not report their experience in Christian terms if it really is Jesus that they encountered, etc.
1. It was not their time for judgement because they returned to life. (Hebrews 9:27) It may be a mistake to assume that their experiences are the same as those who don't return back to earthly life.
2. Isn't this in some ways comparable to a nonbeliever having a positive experience with Jesus during his earthly ministry? I would imagine that he left a positive impression on some people who nevertheless did not become believers, at least not at that time. The encounter with Jesus was not the end of their journey, just one important step along the way.
3. We interpret our perceptions through a lens of prior beliefs and cultural assumptions. That can be the case in near-death experiences as well.
4. Encounters with some kind of luminous being could be encounters with angels rather than Jesus. That may at least change the nature of the experience.
5. I'm also not discounting the possibility of demonic deception in at least some of these experiences.
6. For whatever reason, God has chosen to keep us at a certain distance from him and maintain a veil of uncertainty as part of this life in a fallen world. Whatever those reasons are, should we assume that the reasons are totally absent during near-death experiences? If not, then why should we assume that the purpose of those experiences is to give full clarity and ensure total accuracy?
7. An all-knowing God can have purposes that go beyond the immediately observable effects on a person's life. It would be interesting to study the lifelong trajectory of faith for those who have near-death experiences (rather than what they initially believe about them).
8. Negative experiences may be underreported for various reasons. The person having such an experience may be more ashamed, may be more likely to suppress the memory, etc. Also others may be less likely to pass forward reports of such experiences.
9. Nevertheless, from what I've heard, there is at least a significant minority of near-death experiences that are of a negative or "hellish" kind. I only looked at the abstract, but "A systematic analysis of distressing near-death experience accounts" says "Distressing NDEs represent 14% of our sample". I very vaguely remember that someone found it to be a higher percentage when dealing with patients having cardiac arrest (or something along those lines).
10. There are at least two very different ways to think of what happens during an actual near-death experience. Either it's specifically "designed" by God for the individual's needs and granted by God for that specific purpose or it's some kind of an anomaly, a case of the "normal" course of things in the borderlines of life and death somehow "malfunctioning" so that a person wasn't really "supposed" to experience it. Not that God would make a mistake, but just like the effects of purely physical laws of nature can be sub-optimal and counterproductive for us due to the consequences of the fall, perhaps it's not totally outrageous to speculate that something like that could also have an effect on the "interface" between the natural and the spiritual in some of the near-death experiences. The point here is that if at least some of the near-death experiences are not specifically designed as revelatory experiences for the ones experiencing them, it makes more sense that they would leave the subjects with confusion about what exactly happened.