Their anatta understanding is still inferential, even if they have peak experiences of some aspects of no-self. It is not the same as what we call the realisation of anatman.
It will be good that when doing vipassana, at the same time you contemplate experientially the two stanzas of anatta or bahiya sutta, that will lead to the anatman breakthrough
Also, some recent writing by Daniel on Vipassana in DhO:
JC said "why the need to experiment with all sorts of practices? Why the need for the switch to Zen, Vajrayana, prayer, Catholic devotional practices, martial arts, magickal practices, and so on?
Why not just continue to observe exactly what's going on in the present moment and see the Three Characteristics?
Well, it could be enough, sort of. The Three Characteristics are profound, very profound, staggeringly profound, and not easily grasped in their entirety. It seems perfectly reasonable to grasp them in their entirety by observing them, but there is a problem, actually, that last line contains a bunch of problems that are not obvious until you see them clearly.
I will go by the words in that last line to illustrate the problem.
"Continue": there is no continuing. There is nothing to continue, no past that could be continued, no future to continue into, and this moment is entirely ungraspable. No sensation could ever actually grasp or continue. Everything is fresh but perfectly ephemeral. The notion of continuing, from a high insight point of view, is a serious problem. Instead, there has to be a deep non-grasping, a perfect and flawless appreciation of non-continuing, a deep never could be a continuing, a deep nothing could ever be continuing, a deep sense of not only discontinuity, but of the utter flowing, vanishing, empty transience of anything that seemed to be able to continue. One must figure out how to go beyond continuing, beyond grasping, beyond that strange mental illusion that such a thing could ever occur or have occurred.
"Observe": there is no observing. There can be no observing. There is nothing that can observe at all. Everything is just occurring where it is, naturally, straightforwardly. There is no observer. There can't be any observer. There never was any observer. Deeply understanding this is required. There never was any observation. Observation can't finally do it. One must figure out how to shift out of observing to just phenomena occurring.
The qualifier "in the present moment" is a problem in some way. This almost always involves some subtle or gross pattern of sensations that we refer to mentally when we say "now", or "the present", which are not actually stable, not actually a present, not actually anything but more empty transience, yet we make them seem like a stable present. This is very subtle, deep, profound. Even "the present" doesn't withstand scrutiny, and we must be careful with this sticky concept, as it can itself become a sort of a solidified thing, part of the illusion of continuity, observation, practitioner, etc.
So, while it is true that deeply comprehending emptiness, non-continuity, non-observation, and even non-present, can occur by just continuously observing this present moment, we must be careful, and sometimes it takes people shifting out of their trench of "good practice" to do something that is out from good practice and instead is just the unfolding empty wisdom dharma. Various people find various methods to make this subtle shift, and one size definitely does not fit all, so best wishes sorting out what will help you work out your salvation with diligence.
One could just say that each transient moment, however it is, naturally understands its ungraspable, discontinuous, emphemeral, non-existent, empty nature, straightforwardly, perfectly.
However, one must be careful not to idealize or intellectually reify any of those concepts and qualifiers, and instead this is something that is purely perceptual.
It applies to every transient moment, regardless of any other consideration of the specific qualities of that moment.
All that said, I did, as my last push, go back to the Three Characteristics and Six Sense Doors, just those, but at a level of extremely high precision, inclusiveness, and acceptance, and found that effective. Yet, the place I had gotten to that seemed to make it effective was a radical disenchantment and dispassion towards with everything “I” had attained, everything “I” was, everything “I” could become, everything “I” could experience, and how to arrive at such a place varies a lot by the person.
Vipassana Must Go With Luminous Manifestation
Four Foundations of Mindfulness: The Direct Path to Liberation
Mindfulness as Remembrance