Long answer: The Netflix series mostly focuses on Retsuko's life choices and conflicts. The shorts have a significantly larger cast of co-workers that Retsuko deals with. The shorts focus on those relationships with her co-workers and gives a more in-depth look as to why certain ones seem to annoy her more than others in the Netflix series.
Another thing is that the canon is different in each show. There are characters that get along in the Netflix series that don't in the shorts, characters that have romantic feelings for each other in the Netflix series that don't in the shorts, a lot of line changes between characters, and many more differences. It is accepted that the Netflix series story is the "real" canon and is meant to replace the story of the shorts.