I'll bite.
I'm trans. I transitioned six years ago, had SRS almost five years ago, but I'm still trans. It's not a label, not an identity, not even really how I feel, it's just a fact. The fact is, there are very few people who do or even should know this. Doctors, my partner, my family. It's important that I'm trans when I need medicine or surgery or something else that affects how my body functions, because being trans is a relevant fact about how my body functions, and that's true no matter how long ago I transitioned.
What's happened for me, at least, is that over time I've stopped associated being trans with all of the things one might normally associate with it. It's almost so disembodied to me that I don't even think about it in terms of being 'trans + female'—it's more like I'm trans, I'm female, and those things are barely related. For me, when I think about or am reminded about the fact that I'm trans, it's not "I'm trans because of transition, HRT, surgery ... etc." or even "I'm trans because I used to have this other body and now I have this one" or "I'm trans because I was assigned male at birth" but more like...I'm trans because I'm trans. And all that means is that certain aspects of my body are/behave differently.
As far as my inner monologue is concerned, or about what I think about, I don't even necessarily remember or think about the fact that my body is the result of HRT/surgery and that it used to look and behave differently, it's more like my mind operates in a pretty circular fashion (I'm trans because of xyz traits about my body, I have xyz traits so therefore I'm trans), since that's the only way in which being trans is really relevant to me.
I guess what it comes down to for me is that I didn't transition in order to be trans, I transitioned in order to feel something other than horrible about my body. The end result with the current medical interventions we currently have is a body that still reflects that I'm trans, if not externally then internally. That's not relevant to a whole lot of people, and so as a consequence being trans is not something a whole lot of people do know or get to know.
Aside from the fact that both 'transgender' and 'transsexual' feel somewhat old-fashioned to my ear, I don't really associate it with gender or sex either, anymore, which makes 'trans' a term that makes a little more sense to me and my experience. So despite the fact that 20% of my life has passed since I've done anything related to my transition, I don't feel like the amount of time that's passed makes me any less trans. Maybe it's a little confusing, because I know 'trans' also functions as a community identifier for people who are frequently in earlier stages of their transitions, and the amount of time since I've been there makes it more difficult to feel or express the same degree of kinship or solidarity, but I think of the definition I use for myself as being the same word with a different meaning.
In this sense, I echo Max's sense of it being hard to connect with people in earlier stages of transition, because of how distant I feel from the anxiety and excitement related to first steps. For me though, I feel so far away from transition that my use of the word 'trans' for myself reflects the things that are relevant about being trans now (infertility and daily medicine) rather than the things that were relevant about being trans six years ago (everything related to transition).