State of the Code not Saved

Hi there

I’m working through my first guided project. I’ve saved my work on Jupyter and came back to it a day later. All my code is saved, but it doesn’t run.

When I try to call a defined function I created or perform and operation on a list I get a NameError saying that the function or the list is not defined.

I saved my work like I always do by clicking “Save and Checkpoint”. Any idea why this is happening?
Do I have to “Restart and Run All” ?

If you close a Jupyter Notebook and return to it later and re-open it, you have to run all code cells again.

Thanks a lot for the response. For some reason, I thought I can just pick up from where I stopped last time, which I see now doesn’t make sense.