If you can swing 26k, just get a brand new 2016 Limited. Then you know from day 1 how the car was treated.

definitely the series.blue. you get the jdm underpanels, jdm frameless mirror, sti front lip, sti side skirts, sti rear splats, obviously all the special blue interior but also upgraded knee pads, sti push button, different paint (the white is a tricoat pearl and the wrb is a darker deeper shade) and painted brake calipers.

features that 2015 has that the 2013 doesnt, newer key fob which looks a million times better, shark fin antenna, bigger exhaust tips, better stock suspension, and slightly better engine/trans differences.

I'd say anything built 2/13 or earlier (door jam sticker) counts as an 'early car'.

Big issue is the Direct Injector seals melting, a tune was introduced 3/13 to reduce the knock on shifting and there is a TSB to get a reflash to resolve it, every aftermarket tune has incorporated the fix, and you have to exhibit the symptoms for a dealership to reflash so many people will have trouble getting it.
Good summary thread:
http://www.ft86club.com/forums/showthread.php?p=1056205
Big speculation thread:
http://www.ft86club.com/forums/showthread.php?p=983492

There were some early cars that had timing issues, some running rough, most have been ironed out, issue seemed to be resolved by fall of 2012.
http://www.ft86club.com/forums/showthread.php?t=15577

Those are the two big widespread serious issues, there are smaller things like a handful of transmissions having various issues likely related to manufacturing tolerances and quality control (probably a few hundred replacements happened), miscellaneous engine failures that have no consistent cause, leaky taillights, chirping high pressure fuel pump, a handful of clutches, basically stuff that could still happen to any car.

The two I think are 'unsolved' and still could happen on a brand new car are the coil pack failures and valve train failures.
http://www.ft86club.com/forums/showthread.php?t=30879

http://www.ft86club.com/forums/showthread.php?t=73858
http://www.ft86club.com/forums/showthread.php?t=95210

First off there are probably more 13s without issues than with. Didn't want to scare people and not slamming the 13s but there is certainly some circumstantial evidence that the 13s have had more issues with engines and trannys. The TSBs tell much of the story themselves since there are 10 for 13s, 2 for 14s (both for the same issue really) and only 1 for 15s. Now some of the TSBs certainly apply to all the model years (crickets) but most apply to 13s up to April 2013 so for the sake of this discussion let's call that the "early" 13s. The vast majority of the blown engines listed here have been on 13s but that doesn't mean there is a problem with all of them.

And in reality a well kept 13 with all the TSBs completed could still be better than a 15 that has been beat to crap so any used car is really a gamble anyway. I wouldn't worry a whole lot as my previous comment may appear stronger than I intended.

@strat61caster @Tcoat thanks for the info. I just took a peak at the door jamb and i have a 05/13 car. This is my first sporty Toyota and I plan on keeping it for a long time. It'll likely be my first force inducted car (aftermarket, that i own), and it'll see a lot of track time even in NA form. I know i'm being paranoid but as I've said, I love this thing and want to keep it for a long long time.

To stay on track, the OP can definitely find an unmodified/unmolested low mileage '13 just like i did. It's a matter of being patient. I'm not a fan of buying modified used cars. A '13 with performance mods seems like a gamble. Good luck either way.

I'll take a car with sticky tires and an owner who changed oil before and after every track day than the 'old lady driver' who forgot to get the oil changed until 15k and it was done by the service monkey who stripped the drain plug and put sealer on it so it was 'future dealer service tech's problem'

True. I guess it's a gamble when you don't know either case.

I'm going to try to get the Series blue for around 26k before taxes. In CA that seems to be as low as that car will go.