Bianchigirll (BTW, why are there two "l"s?), by 1991 the Canadian and USA models had been consolidated. My 1991 Canadian catalogue appears to be the same the 1991 USA catalog. Perhaps it is from some other foreign market?
Given, that you suspect repainted stays and forks, and the majority of the decals are missing, it may be possible that the downtube decal is a replacement and maybe even the whole frame is a repaint. If I was asked to make a educated guess based on the serial number alone, I'd say it is an Italian model, based on the two distinct segments. My guess would be that B = Bianchi, O = fortnight and 0 = calendar year = 1990. So it's possible that this may be a 1991 model manufactured in late 1990. If I'm correct, this would seem to imply a foreign model, as the only domestic models that were probably made in Italy would have been the Proto and Pista, which it obviously is not.
I also noticed that, while it may use use a 1991 8 speed brifter set-up, the brakes are single pivot, meaning they are older. So, the components may not be original.
I'd be interested to know:
1. Is there an obvious difference between the 2nd and 3rd characters of the serial number (i.e. one an "oh" and the other a "zero")?
2. What size is the seat post?
3. If there are any ridges on the inside of the bottom of the fork's steerer tube? If so, how many are there, and are they straight or spiral ridges?
4. Are there any signs of underlying paint on the fork and, if so, what colour it is?