Blorb - OAI includes TBN while Blackstone charges you an additional $10 so you do get more bang for your buck. For more info on oxidation and nitration, check out this pdf:
(page 11)
https://www.amsoil.com/lit/g2047.pdf
Oxidation measures the breakdown of the lubricant due to age and operating conditions. Nitration occurs when nitrogen oxides react with the lubricant, causing deposit formation and an increase in viscosity. Note that oxidation and nitration readings do not begin at zero.
OAI will do a fuel reading by gas chromatography if you request it but I don't think it's needed on a stock 86 with the excellent multipoint injection. It would be more useful on an aftermarket tune to see if you're running rich. OTOH, a WRX OAI uoa typically shows ~2.5 -~5.5% fuel dilution.