Select your Exam19 sheet then on the Home ribbon in the Editing section, click Find & Select, click Selection Pane.
Is what shows the name the button on that sheet should have?
Also, all the sheet names have a space between Exam and the number except for 19.

You can also see the button name by right clicking on it and the name will appear above the row numbers.
This is where you can change the name.
Using that Selection Pane allows you to just click on another sheet to see the names they have.