A Stunted Childhood and a Can of Fancy Mixed Nuts - S2-E10
Corrected entry: Sheldon sees a billboard on the joke rack, where it says "it's a bazinga." In the corner of the board, it says Toledo.com, wrong for 1990.
A Crisis of Faith and Octopus Aliens - S2-E3
Corrected entry: The episode is set in 1989, but they discuss the movie Ghost which did not come out until 1990.
Correction: Not necessarily; since the second season has begun, they could have progressed to 1990 by this point. It also hasn't been established whether he's had his tenth birthday yet at this point in the series.
Sheldon's birthday is Feb 26, 1980.
I knew his birth year had been established already on BBT; I just didn't know for sure if the date he had a birthday within the parent series corresponded to the "real" world because BBT time only roughly coincides with real-world time in most cases.
While a BBT season may not be a full year or the next episode isn't set one week later (like many sitcoms), because the show relies on pop culture so heavily, like releases of films, etc, I do think BBT is set in the real life timeline, even if a holiday special is set in the "future" (e.g. a Halloween episode is aired 2 weeks before Halloween.) However, with YS being set in the past it can be hard to tell what the exact date is, unless specifically said, and you have to rely on context clues (like a lot of shows set in the real life timeline past). I only replied with his birthday so others could make a decision if the correction is valid. I do not know enough about the episode to know when it's suppose to be set or how long it's been since his birthday (as I did think he was suppose to be 10 in the episode).
Correction: It says "Toledo, OH" as in Toledo, Ohio where the company would be based.