Mary tells Charles at the party that she and Caroline had discussed her present and decided to buy back the violin he had pawned. However, earlier when she and Adam were getting ready to visit the family, she said she believed they had all forgotten her birthday and had no idea a surprise party was planned.
Mary is said to be having her 16th birthday in this. Born in 1865, it sets this in 1881. Grace, born in 1877, only appears to be a year old but would've been 4 years old in 1881.
At 21:46 Albert is shining Standish's sons boots. He is standing on the boardwalk and the boots are shiny. He then takes one step off the boardwalk and his boots are already caked with dust and dirt. There is no way that one step would cause boots to get that dirty.
At 22:10 Laura pushes Standish's son and he falls down. When he stands up his right knee is dirty. When he is standing and reaches into his pocket to give Albert a penny, his pants have no dirt on the knee.
At the end when Mary blows out the candles on her cake, some of the candles were burnt down to nothing. When they show Laura pulling the candles out of the cake, the candles are a lot taller than they were when Mary blew them out.
Albert is sitting in Pa's chair smoking Pa's pipe. For several minutes, Laura is somehow completely unaware of the pipe being smoked until she walks over to Albert and sees him when she should have easily been aware of it after only a few seconds.
Albert's "place" is twice the size on the inside than outside. It's noticeable when Charles visits.
Mary Ingalls birthday is January 10th, everyone should have been wearing coats because January is a winter season month. Charles Ingalls would never forget Mary's birthday because he was born on January 10th also.
As the final shot of the scene of the whole table, where Charles is playing the fiddle, Willie is nowhere to be seen, but seconds before, he was seen sitting between Nellie and Harriet.
This show took place in 1877. Laura said Adam loaned her a Braille writer. But that device was invented in 1892.
The wrapping paper on the fiddle box wasn't invented until 1917.
The tune Charles is playing on his fiddle at the end of the episode is more than twice as fast as his bowing can support.
It was not explained how Caroline got the money to get the fiddle back out of the pawn shop.
Harriet Oleson said that Dr Baker prescribed alcohol for some of his patients. This is incorrect. It was Dr Logan.