The racetracks in the film have modern synthetic track surfaces, not the dirt surfaces that would have existed at the time of Secretariat's races. The exception is Churchill Downs, which is still dirt.
When Secretariat is led to the track before the Belmont Stakes, someone in the crowd takes his picture with a Kodak Instamatic camera, with a FlipFlash flash device on it. They were first produced in 1975.
The credits say that the Scripture at Mrs. Cheney's funeral was New International Version. Mrs. Cheney died in 1969. The New International Version Bible was first copyrighted in 1973, and was not widely used until several years later. The funeral scriptures were likely the King James Version, which was widely used by most pastors in most mainstream denominations at the time.
In late March 1970 ,just before Secretariat was born, Penny gets a call at her home in Denver from Eddie that the foal was about to drop. In then next scene her children are playing in the backyard pool, and the leaves on bushes/trees in the yard are green. In late March 1970 the average daily high temperature was below 50 degrees. The trees were bare, and kids most likely weren't swimming in the backyard pool.
When Penny and her rival owner trade barbs at a press conference, Penny says the other owner's horse has as much chance of beating Secretariat on the track as he, himself, has of beating Muhammed Ali in the ring. In spring 1973, George Foreman was the boxing champion, and Ali was considered quite vulnerable.
As Secretariat is being walked out of the paddock before the Kentucky Derby, a little girl takes his picture. Miss Hamm says, "He's posing again!" but the movement of her lips doesn't match the words she is saying.
Before the Belmont Stakes, when Secretariat is being led to the track, someone in the crowd takes his picture with a Kodak Instamatic camera, which would make just one "click" when the picture is taken. The camera makes the sound is that of a single lens reflex (SLR) camera.
When Lucien, Penny and Ronnie are in a restaurant talking about Secretariat being declared Horse of the Year, the cook says he needs more meat because, "These little guys eat like elephants." A jockey's livelihood depends on weighing no more than 120 pounds. Active jockeys exercise obsessively and follow very strict diets.
Eddie Sweat was holding on to Secretariat as he washed him. But when Penny Chenery comes over to help wash him, he's no longer holding onto him, it looks like someone off camera is now holding onto him as you can see the lead moving. And then when Penny moves off towards the foaling shed, Secretariat is now ground tied, no one is holding onto him.
When Penny's family is watching the Preakness on television at home, after Secretariat wins her son reaches into the bowl of popcorn sitting on the table and throws hands full of popcorn in the air. In all the shots leading up to the win, there is no popcorn on the floor or table, but in the shot where he reaches into the bowl, there is already popcorn scattered all over the table and floor.
When they are training for the Belmont, Penny Chenery is shown to be turning towards the left to lean her back on the railing while saying her line about how Pancho thinks they are training too hard. The shot cuts to a camera on the left, and we see the whole turn again from that angle.
When the jockeys are mounting their horses prior to the Belmont, Sham's jockey says to Ron Turcotte "You're going to eat dirt today Ronnie." and the crosses his arms as Turcotte walks away and says "I don't think so." under his breath. The next instant Sham's owner is talking to Sham's jockey and his arms are no longer crossed.
When Penny's brother and husband confront her about the inheritance tax, she ends up calling Ms. Hamm into the room. The door remains open behind her throughout the scene. When Ms. Hamm turns to leave, she has to open the door to exit.
When Penny Chenery (Diane Lane) asks Miss Ham (Margo Martindale) to talk to trainer Earl Jensen in the stable in private, Miss Ham exits out the stable door, the inside shot shows nothing but a row of windows to the left of the stable doorway. When Miss Ham hides just outside the same stable doorway there are no windows, but there is equipment and hay hanging from the doorway.
During the Kentucky Derby race, stable-hand Eddie Sweat is first seen in a crowded area, apparently under cover. When the horses reach the front stretch, he's seen on the rail in the sun. Then after the finish, he's back under cover in the crowd again.
When Penny is being confronted by her brother and husband regarding the inheritance tax. The brother is sitting on the edge of the desk while Penny is sitting on the edge of her chair with her elbows on her knees. As the conversation continues Penny is suddenly sitting upright in the chair with her hands in her lap.
The police officers at Aqueduct race track wear Nassau County uniforms. Aqueduct is located in Queens, NY, so they should have NYPD uniforms. Belmont Park is located in Nassau County, which is not part of New York City.
Penny Chenery meets Ron Turcotte for the first time when looking for a new jockey for Secretariat. In real life, Turcotte had ridden for her many times before, including winning the Kentucky Derby the previous year on Riva Ridge.
In the film the announcer for the Belmont Stakes mentions the margin of victory being 31 lengths which was true, but in real life announcer Chic Anderson announced it as 25 lengths because he was unable to correctly estimate the distance between the horses due to the incredible lead Secretariat had.
Lucien Laurin berates and fires jockey Paul Feliciano after Secretariat loses his first race. In real life, Feliciano rode Secretariat in his second career start, which he won, before Ron Turcotte replaced him.
In the movie, Secretariat trails the Kentucky Derby field for the first half of the race then stages a dramatic come from behind win. In the real Kentucky Derby, Secretariat was third from last around the first turn and sixth down the back stretch. He made a great charge over the last 3/8 mile but it wasn't quite as dramatic as in the movie.
The movie depicts Chris Chenery dying of a stroke, followed almost immediately by Bull Hancock simply falling over dead. In fact, Hancock died at Vanderbilt University's hospital of pancreatic cancer in August 1972 and Chenery died in January 1973.
When Secretariat is shown coming around the final turn at the Belmont stakes, there are a number of photographers along the rail taking pictures as he passes. There are three concentric tracks at Belmont with the Belmont Stakes being run on the longest, outer track. There were no people standing on either of the inner tracks and therefore, no photographers along the rail during the actual race.
When the Belmont Stakes is being run, it appears to be in the autumn, as the trees in the background are changing colors. In New York this generally occurs in early to mid-October. The Belmont Stakes is run in June, and the trees should be an intense green.
When Penny's family is watching the Preakness on TV, a photograph of Secretariat can be seen on the desk where John is sitting. It is the iconic photograph of Secretariat and his 31-length lead at the Belmont, which would obviously have not happened before his victory at the Preakness.
In the crowd, in 1973 when Big Red is being brought out to the gates, someone is holding up a sign that says "I 'heart' Red", with the red heart logo. In 1977, William S. Doyle, Deputy Commissioner of the New York State Department of Commerce hired advertising agency Wells Rich Greene to develop a marketing campaign for New York State. Doyle also recruited Milton Glaser, a productive graphic designer to work on the campaign, and created the "I 'heart' NY" design based on Wells Rich Greene's advertising campaign, where it then began the "I 'heart'" popularity across the country and world. Of course, none of this means that it would have been impossible for an "I 'heart' Red" banner to have appeared in 1973.
In 1969, the family drives to the Virginia farm in a blue 1961 Chevrolet Bel Air with Virginia plates. When they are preparing to leave, the husband says he had the flight moved up. When all except the wife leave, they do so in the same Bel Air. A 1961 car would not have been an airport rental car. It appears they drove from Colorado to Virginia.