Hey Sam,
I knew I recognized your name from somewhere, it's interesting to see you come back with a similar sort of question but I also suspect that I may know why. You mention in this post that this shift happened 9 months ago, and, given the fact you're first post was 2 months ago and described something 7 months before that, I'm assuming we're talking about the same experience again?
If so, the way I see it is this: You might have gotten Path and have been in Review when you posted, hence the Dark Night cycling stuff and the continual recurrence of Equanimity with little effort. Also, as Daniel says, what you describe phenomenologically is unlikely to be down to an A&P Event, especially since those changes and improvements in your quality of life, and practice, have remained the same since.
It may be that trying to align your experience with the MCTB and Theravadan models is only adding to the confusion, especially if you're more interested in a Mahayana perspective. In that case, I highly recommend Thusness and An Eternal Now's blog, especially
this article on Thusness' model of awakening. It's the guys own take on it but it's very useful for another way to analyze these experiences and has been of immense use to me over the last year.
I got Path without even knowing what the hell a Path was so I can totally understand where you're coming from, it's not that I didn't notice this incredible and utterly unquestionable, sustained and effortless change in experience - the instant it happened it was crystal clear that
something was very, very different - but it wasn't until I came to the DhO and MCTB that I learned it was most likely Path. Also, having not come from a Buddhist background it took me a long time to understand what those perceptual changes were and what was now apparent in experience, especially subtle aspects of the subject/object duality which still remained and how to penetrate deeper into not-self and impermanence.
Your practice is solid and I remember commenting on the quality of your descriptions before, I don't doubt that you've attained some sort of permanent shift at a fundamental level but it'd be interesting to know how things are for you in terms of how you experience a sense of existing.
How would you say things were in terms of a sense of Self still existing?
How do you experience sensations from moment-to-moment, i.e. how do they appear?
Do you notice anything still implying a subject/object split in the field of perception?
Does there seem to be a background to experience of any sort?
Just a few things to look at to see what's still there to be seen clearly. Either way, kudos on whatever the hell it was and it's great to know that, regardless of what it was, you're happier and more content in life now. It's worth keeping a practice journal of some sort if you don't already, even if it's just writing it down at home after a sit, just so you've got something to refer back to 'cause, in my experience, sometimes these shifts take away stuff you didn't even notice till you realize it's not happening anymore!

You still mainly doing shikantaza?
T