There has been a minor update to the algorithm calculating your storage costs. Previously every single asset file’s storage size as well as every individual file within all your packages have been summed up. You can see the sum of all that on your account page (in the Package/Asset Storage row).
Starting today you only pay for each unique asset file as well as each unique package file. So if you upload the same asset file twice using different filenames, you’ll only pay for storage once. Similarly if you import the same package multiple times (or if different packages share some common files) you only pay for each unique file once.
This change will probably not have a big effect on most users but can make some use cases more viable (like automatically created and updated packages). Note also that this change can only result in you paying less. It cannot happen that you pay more. Enjoy.