TCI was introduced in the 594 in late 2019. Late October or early November. Anything before that will not have TCI treated pickups. As for difference, there is definitely something there. It's hard to put in words, but they just bring something more to the table. Clearer sound, more articulate. I don't know. They're good, but so are the non TCI 58/15 LT pickups. You can't go wrong either way.
Here are some comments from another thread. MA Pete is the "594 expert. I think he's probably owned more than 50 of them.
With respect to the 2020 594s; yes, they still have the LT pickups, just with the TCI treatment. I don't know if it's the nitro or the TCI, but there is just something "different" about them. I'm really bad at this stuff, but I'll cut/paste some thoughts from MA Pete. First, realize his Holy Grail guitar, after lots of PRS and other brands, is his 2016 PRS SC 594 Prototype. He is on record stating that the 2020 Core SC 594 are just as good as that Holy Grail. From a confirmed tone cork sniffer, that says a lot. Here's something from Pete:
In the coming days, this guitar blew my mind! It validated some really important things about the new 2020 models. First and foremost, the tone and feel of these 2020s (at least THIS ONE so far, more to follow) was 90-95% as good as a Private Stock 594. That was not at all the case for the many V12-finished 594s I owned in 2016 and 2017. They were all on average really fantastic, but none really held a candle to the Private Stock ones, for me. I really love everything about the PRS Nitro finish, both in feel, and also re my opinion on how it positively affects the resonance and tone of guitar, so I am biased in that regard. (Having owned a pretty broad range of Core, WL and PS guitars over the past 12 years, over 100 of them, I feel pretty qualified to weigh in with an opinion on that.)
Also, the TCI pickups are the "Real Deal", and also these new 5815 LT+ pickups specially wound for the SCs are amazing. (I will go more into the pickups on a subsequent post.)
I have come to really love the tuners, everything about them - well, except that they aren't locking tuners.I dislike restringing a guitar with vintage tuners as much as the next guy, but these tuners just look so "right" to me on the 594s, so much so that the Phase III tuners now look "wrong" to me. Also, they look and feel high quality IMO, despite being some sort of plastic. They are more solid mechanically in feel than the Phase IIIs. Significantly more so. If I were to spec a Private Stock 594, there is no question in my mind that I would spec it with these versus the Phase IIIs.
When some of the Chicago crew came over on Feb 15, we did an A/B of the 2016 and 2020 Prototypes, and the gang unanimously declared the 2016 one bested the 2020 one re Classic Singlecut tone, at least by a little. I think it is pretty close. Over time, I have come to like the 2020 one a little more, it certainly gets played more. The 2016 one is a keeper for sure, it is so special in what it is, but what an awesome discovery with regards to the magic of this first 2020, that it can be considered pretty much as good as the 2016 Prototype is amazing!
Finally, if you haven't seen this video yet, check it out.
I think it has been readily proven when that video was released that is not a real 1959 sunburst guitar. Regardless, they both sound great.