This drawing most likely refers to animation mistakes in The Million Dollar Cat, chronologically the next Tom and Jerry cartoon released after "Zoot Cat" and the one where a telegram is the major plot device.
"The Million Dollar Cat" had a release date of May 6th. I don't know how far along in the production process the film was on February 25 but to warrant the expletive-laden bawling out delivered above I'd guess that the mistakes were discovered after it came back from camera. I didn't spot any scene where the telegram should have appeared but didn't, so this mistake was probably fixed.
There isn't any actual gravy anywhere in the cartoon. In this scene, Jerry reappears after having thrown himself out the window and eats Tom's breakfast.
He finishes by mopping up the plate with a slice of toast. Maybe what is meant by "gravy left off" is that there should be some runny egg yolk on the plate for Jerry to wipe up. If this is the gravy mistake, it obviously wasn't considered worth fixing.