Here's how I understand the model. Warning: highly geeky.
First, two more technical terms: "cutting edge", and "center of gravity". The cutting edge is the most advanced nana/jhana you have accessed. The center of gravity is somewhat behind that, where "you" are most of the time. This is where the "early" and "mature" sub-nanas can be understood on the map: "early" a&p, for example, is when you can get there (cutting edge advances into A&P/second Jhana), "mature a&p" is when your center of gravity is squarely in there. this applies to later stages, too; and this is where the nana vs. jhana distinction comes in handy: jhanas are fairly stable, places where the center of gravity can "come to rest". Thus, A&P and Dissolution and Equanimity have "early" and "mature" stages, because they correspond to second, third, and fourth jhana; while the Dark Night has no such resting place, being composed entirely of unstable nanas. (To be really geeky, the third jhana can also be understood to span all of the dark night).
So in each sit, you progress up past mind and body (first jhana) to the territory between center of gravity and cutting edge, dig around there, back and forth, push at the cutting edge, tug at the center of gravity.
Still with me?

Now, the talk of backsliding is largely about two experiences: the perceived gap between "cutting edge" and "center of gravity", i.e. I could access A&P yesterday but can't today; and the slippery territory between dissolution and equanimity, where the cutting edge might reach equanimity but the center of gravity just won't stick anywhere, giving the the impression of backsliding, swinging on a rope and so on.
Okay, but one day, the center of gravity sticks in early equanimity, cutting edge advances, and one fine day, they both end up in high equanimity, and eventually, the thing pops, stream entry, bingo.
The pattern now shifts: With each sit, you can drop into A&P, second Jhana, directly, progress up to equanimity, and, with sufficient intent and clarity, review the fruition that marked stream entry. Or you could do concentration work, or fuse the insight and concentration sits, or whatever. This is calles "review phase" in the map.
You'll probably also notice how you're going through the cycle during everyday life. Maybe you'll experience fruitions off cushion. Maybe you'll just notice the deeper insight resulting from the fruitions. Whatever.
So that was one pass of the map, one Path of Insight, including the backsliding prior to path moment, and the cycling after. This is also one of the reasons why people occasionally talk about fractals: there is the large pattern, which seems to be composed of smaller versions of itself, peak of a&p, trough of dark night, plateau of equanimity, jump of fruition.
Now this patterns repeats for second path, third path... this is where the nice model seems to break down. After third path, it branches out, looks like a huge self-similar fractal (the other way people talk about fractals), has all kinds of traps and seductions, and in the end, I'm told, the cycle model, while still kind of applicable, is just too primitive and unhelpful, or it has to be taken to another level, or whatever.
Still reading?
Here's my experience so far:
I hit A&P as a kid (including subsequent dark night), and repeatedly again during teen-age and during early adulthood. When I came across MCTB, I was able to gradually see my experience in light of this map, and make good progress up to equanimity. I then got too hung up on the maps, chased strange experiences wanting them to be Formations or the Three Doors, and spent a good year spinning around in the territory between early equanimity and A&P, i.e., the Dark Night. But in the end, and with the help of all the good people here at DhO and sister sites, I entered the stream. Now, I can see how very accurate the map to stream entry is, but also how misleading if mistaken for the real thing.
Thus I appear to talk away from the maps, just like many people before me did after they made it here, and doubtless many after me will, once they get here. But that's just Concerned Parent Talk. Really, don't listen to me, use the maps to your heart's content, and in the end, you'll have learned how they work and what they don't do for you.
I hope that was helpful in some way.
Cheers,
Florian