Chapter Six: E Pluribus Unum - S3-E6
Factual error: When the Russian requests the cherry flavor and refuses to talk, he gets thrown out. At the back is an oil drum from the French energy company "Total." However that logo was introduced only in the mid 2000s. (00:11:55)
Chapter Six: E Pluribus Unum - S3-E6
Continuity mistake: When the librarian picks up the phone he picks up the one in the middle, in the next shot we see he has the one to the left and when he hangs up it's the one in the center again.
Answer: The body was fake, made by the scientists at Hawkins Lab in an attempt to cover up his disappearance and the existence of the Upside Down.