The town sign, throughout the series, says "Walnut Grove, Founded by Lars Hanson, 1840". The bond Harriet finds says Walnut Grove Bond and is dated 1835, which would be 5 years earlier than the founding of the town.
After Nels agrees a rematch at a later date, they leave the table, in the next scene the pieces on the board are not in the starting position as they were in the previous scene.
The little white house with the astroturf garden where Jess and Etta live was previously seen as the house of Miss Cooper and Toby Noe.
The red dress Mrs Oleson wears at the 10 min mark is made of the same floral calico fabric as the dress Laura wore at her first teaching job.
The Hanson house was given to the blind school which eventually burned down. There was almost nothing left of it. Strange that it seems to have grown back.
Laura would not have been a member of the Town Council, as shown, as a woman could not run for the position at the time.
The numbers on the chalkboard behind Harriet are meaningless.
American Beauty roses are pink, but the one Floyd show Lem is red.
Lem McCary claims to have been Lars Hansen's best friend, and helped to found Walnut Grove, yet he was never seen at any point before this episode.
Mr. Hanson's house was given for the blind school, which subsequently burned down. Therefore, Harriet wouldn't have had accessed to his house.
If George Maddox was long dead in his cabin, then Lem and Almanzo would have smelled the body upon arrival.