The reason you shouldn't have any text within .375 inches of your cover's edge is that the printer needs a margin. They won't hit the cut exactly right every single time with Print-On-Demand. The book cover designer should be able to adjust this for you. Or if you designed your own book cover, adjust the text on the image.
When you use the Amazon KDP Cover Templates they will show you the exact gray area that you cannot have any text within:
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KDP Cover Templates: https://kdp.amazon.com/cover-calculator
Best of luck!