In the tree house Sam and Teeny are talking about families and mention the Partridge Family. The Partridge Family (1970) would not debut until September 1970, but the movie is set in the summer of 1970.
In the summer of 1970, the girls ride their bikes under a railroad trestle on which gray tanker cars are passing with the Norfolk Southern Corp. logo (leaning "NS" with horizontal stripes), but that company did not exist until 1982.
Badfinger's song "No Matter What" had not been released in the U.S. by the summer of 1970. The song had been recorded in London in April 1970 but was not considered for American release until a U.S.-based Apple executive heard the song. The single was released in the U.S. in November, 1970. The LP the song appears on, "No Dice", was also released in the U.S. November 1970.
The Gaslight Addition neighborhood is actually the Country Walk neighborhood in Savannah, GA. The earlier scenes of the movie are set in 1970, but the houses used in the movie are architecturally characteristic of and and were in fact built in 1990.
At the softball game, one of the girls calls a boy "nerd-o". Although the term "nerd" had been around for years before, it didn't become popularized until its use in the sitcom "Happy Days", which aired 4 year later than the time depicted in this movie.
In the movie they say that their home town is Shelby, Indiana. Shelby, Indiana is in the north western part of Indiana. They went to Greenfield, Indiana to go to the library, on their bikes. That is impossible: they are approx 150 miles apart.
When the girls are looking for articles from 1945 in the newspaper Roberta finds an article about her mother's death. Her mother would have had to have died after 1958, therefore Roberta shouldn't have seen the article unless she wasn't actually searching in 1945 like her friends were.