The previous week, the Ingalls lost all their chickens to the pack of rabid wild dogs. They are poor, and no valid explanation was given as to how they got all their chickens back so soon.
Fingerprinting for crimes did not start until 1891 and the first country to use it was Argentina. It quickly spread across the Spanish speaking countries. However finger printing was not used in the United States until 1901. So Laura, Andy, Nellie, and Willie using flour to look for finger prints to find the "creeper" couldn't have happened and even if they found fingerprints who would they have known who they belonged to anyway. It is not like they had a file of fingerprints on hand of the people of Walnut Grove and the surrounding area.
Ham and eggs 3 times a day is the worst possible diet for a recovering heart attack victim.
Miss Beadle would not have gotten the test results back on Sunday, and if she had there would have been an announcement in church.