Dr. Marvin appears to have been working as a doctor in the Walnut Grove area for his whole career, but doesn't appear until now.
Doc Baker's shingle had been nailed to the wall outside his office previously. Now it is seen nailed to a trellis.
Near drowning does not make someone stutter. Bad premise.
Yellow daisies have no smell.
Laura is seen pitching straw next to some sort of garden with no fence around it to protect it from every rabbit, deer, elk, antelope or other garden-munching varmint on the prairie.
Mrs Oleson's red dress is made of the same floral calico fabric as the dress Laura wore to her first teaching job.
Jenny is shown rescuing an injured Eurasian collared dove on her way to help Dr. Haynes with his gardening. However, these doves did not appear on American continent until the 1980's; they apparently escaped captivity in the Bahamas in the 1970's, and then were found in Florida a decade later. The mourning dove, a close relative, was native to the Midwest.
At the swimming hole, Willie is wearing a modern 1980s shirt with white trim that is not accurate for the 1880s time period.
Ring-necked turtle doves are native to Africa and may be found in Florida. Not likely to be found in Minnesota or for that matter California where this show was filmed.
If Marvin was a second doctor in town all these years, then Doc Baker would not have needed to hire Dr LeDoux in a previous episode.
The story should have contained a segment about Jeb returning the locket Jenny lost.