Is it possible to partly reach a stage or is it always all or nothing?Yes, a yogi could partly reach a stage and go back down to a lower nana and then make one's way back up. A momentum is key in continuing to cut a path through the nanas to the 11th then on to a cessation moment. At times, you may feel like you are regressing. But this is how it works. At times you fall back to nanas you have already passed through and then work your way up to your cutting edge (the highest nana you have reached) As you go up and down, you cut out more of a path upwards till insight matures in each nana. It's all part of the process. If you maintain a momentum in your practice, there is no regress. It just feels like that soemtimes. Momentum and patience and continued application of the vipassana technique is key. U Ba Khin used the analogy of a person swinging on a rope to cross the stream and reach the other side. They swing back and forth each time getting a little more height until they have enough height to let go and reach the otherside. This is essentially what you are doing as you practice moving up and sometimes down the nanas. It's all progress. Progress does not depend so much on how "good" and "peaceful" you feel. Soem nanas suck arse and you feel like shit. But if you continue practicing regardless, you move through them. So if you suffer an attack of "hating meditation" it may well be stage related. Same with wandering mind, agitation, sadness etc....if you keep that it mind, you wont consider it regress, but actual progress. Keep swinging back and forth and get more and more height each time you swing towards the other side (stream entry)
Could I be in a mixture between 2 or 3 stages or is it always clear cut? You could be moving back and forth and at times it feels like its a mixture. Some yogis get to really learn how to recognise where they are on the map. Others don't. If both types of yogis continue gaining momentum, they make the same progress regardless. don't stress over where you are. Just keep maintaining a momentum. At times, it's hard to tell...and other times, it may be easier to tell...the AP soemtimes is real obvious and maybe the 11th too after passing through soem negativity. You'll develop a knack for it. But if you cant tell, dont waste time fretting over it. Just keep sweeping!
Can one partially be at the stage of equanimity, or have had an A&P event that is not so profound as all the lights and everything?Yeh, At Equanimity of formations, there seems to be differing degrees of it. Here and elsewhere they talk of it having three levels to it, low, mid and high. And this is my experience too. One could feel very equanimous at the AP stage too, and soemtimes yogis think they might be at the 11th when they really are at the 4th. You will soon find out, cos the dukkha nanas will be on the 4th and 5th's heels. But essentially it's the same advice...keep practcing vipassana. Yeh, and AP could occur at varying degrees. Soemtimes you only know you went through cos you start feeling like crap.
"The Arising and Passing is like a fart. Sometimes you only know it happened because you smell something. Other times it's an explosion." Bill Hamilton
I have had a few moments in my life prompted by body work of extraordinary sobbing and a great feeling of lightness afterward. Also, when I was much younger I experimented a bit with LSD. I suppose I could have had an A&P event then? Yes, possibly. Some yogis wrote about there experiences triggering an AP event through drugs here Look at Testimonies of the A&P: http://thehamiltonproject.blogspot.com/
I don't know, these stages seem so clearly laid out but I feel like I have no idea. Does it really even matter?Continued momentum in your practice regardless of what arises is what matters if you want to progress on upwards.

So don't worry about not knowing where you are. Figuring it all out can take awhile, and with practice a yogi can start recognising the nanas. A yogi doesnt even have to recognise them to get stream entry though. It helps, but it isnt necessary.
It helps when you feel lost to know there is a light at the end of the tunnel if you keep practicing non-stop.
Hope this helps,
nick