Evelyn finally meets up with fellow contestants sometime in summer of 1963, where Dortha gives her entry form for a Dr Pepper contest. But closeup of entry form shows space for entrants to write their ZIP code, a new concept just introduced in July of that year, which did not appear on order blanks, etc. until well into 1964 or beyond, as many people did not understand what it was - certainly not just a month or so after it was introduced.
The all-weather pith helmet that Ray the mailman wears when the milkman came collecting would not be introduced until the 1980s. Though pith helmets have existed since the 1840s, they were made of cloth or cork. His was obviously wearing a modern plastic one.
On two different occasions, the characters talk about the radiator in the Ryan family car. They pronounce it with an A sound as in "hat". People in Northwest Ohio and Northeast Indiana do not say rAd-iator. That is largely a Philadelphia / South Jersey pronunciation.
At one point, the characters watch an actual clip from an actual Miss America pageant in which emcee Bert Parks asks a contestant about that year's presidential election. But shortly afterward, a sequence is identified as occurring in May 1960. Because the Miss America contest was always held (at that time) in September, this clip would have to be been from an earlier pageant (probably 1959) - which was not an election year.
In her book upon which this screenplay was based, author Terry Ryan indicates that during the shopping spree Evelyn Ryan was prohibited from taking more than one of any individual item however in the filmed spree the Evelyn character grabs two, three or even more of many items like lollipops, candy, pineapples, etc.
In the movie, Kelly and Evelyn Ryan both have red hair. However, only a few of their children have red hair, the rest have brown. This would be genetically impossible since the gene for red hair is recessive; two copies of the gene are needed for red hair. If the Ryan parents were true redheads, all of their children would have some variation of red hair.
Shortly after film begins, there is a head-on shot of Evelyn sitting at a typewriter filling out a full-page entry blank for a Dial Soap contest with form entered into typewriter carriage so audience can read details near top of page right-side up. However, if this was actually the case, she would be typing her entry onto the bottom of the form upside-down.