At some point between the time that FDR gets into his wheelchair and he starts working with his crutches, his bed gets made despite no one having been in the room that would have done it.
In 1924, Franklin D. Roosevelt receives a letter from Al Smith requesting that Roosevelt officially nominate him as the presidential candidate at the Democratic National Convention. In reality, Smith was not the Democratic candidate in the 1924 presidential election but the 1928 election. Roosevelt gave the nominating speech at the 1928 Convention.
Phineas and Jeffrey return to Hollywood after Roosevelt walks on his lawn. Phineas says it is 1929, and then Jeffrey picks up a copy of Variety. Its headline reads: Jazz Singer Pic Pulls Boffo Biz. The Jazz Singer was released in 1927, so the year 1929 was a mistake made by the script writer. There would not be an article written two years later stating The Jazz Singer was making huge profits.
As the Voyagers drop into the court room, the extra playing a spectator flinches, but pretends not to see them.
As the two cars pass each other in between the buildings on the studio lot, a crew member is clearly seen in the rear passenger window of the car.