Factual error: During the big Newsies rally when Medda is singing "High Times", as she is swinging, lighted exit signs can be seen. I don't believe that those were around in 1899.
Factual error: When Jack Kelly and David go to see Spot, Spot is wearing a jacket with his sleeves rolled up. When he shakes Jack Kelly's hand, you can see the tan line from his watch.
Factual error: In "Santa Fe," Jack sings the line "Far from the lousy headlines and the deadlines in between." The word "deadline" was not used in this sense until the 1920s (the movie is set in 1899).
Answer: During the "Two for a Penny" sequence in Carrying the Banner, you can see Crutchy dancing in one of the back rows on the right without his crutch. You can also see him walking without it behind David during the first Sieze the Day when David sings "Arise and seize the day!"