90 spec 16v's can run on normal unleaded if need be, they actually have a different ECU than pre90 16v's. but you'll wanna run it on Super Unleaded anyhow for the extra get up n go!
as for dates, i know somebody in Belfast who has a Jun 92 Oak Green 16v. so they are out there. his also has side impact bars!!!

dont see many on them in a mk2!
onto buying. as everybody says. dont just jump at the first one you see. take your time and look around. bodywork is the main problem, the engine is bullet proof. no real need either for a full service history. a part service history is fine. you've gotta remember that the cars are now appraoching 15yr old. so people aint gonna pay VW service prices!
tbh there is no point paying a massive premium for as late a car as possible! i recently sold my 91 16v as it was rotten in below. outside there wasnt a mark in it.
i then went an bought an 89 16v and it is 100 times better than the 91 16v. it was given a full respray just under 2 years ago and really is faultless. i paid decent enough money for it considering it came with factory leather & BBS splits. but is still miles below 2750!!!