When you upload a PDF to the system and convert to an issue, you use an upload license. 

As soon as you upload, the 12 hour grace period begins (see IMAGE 1)

This grace period is the time during which you can delete the issue, recoup your upload license back to your account so you can use it again (see IMAGE 2)

If you delete after the 12 hours has passed, you WILL NOT get that upload license recouped back to your account (see IMAGE 3)

IMPORTANT: Always be sure to review your issue thoroughly during the 12 hour grace period, so if there are any major problems (missing/extra pages, typos, conversion problems) you can delete the issue, and recoup your license back to your account.  At that point you can make any changes/updates to your PDF and use that license again to re-upload.

You can always replace up to 30% of the total pages of your publication, but if there are problems that affect more than 30%, be sure to delete within the 12 hour grace period so you can use that license again after re-formatting your PDF

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IMAGE 2

IMAGE 3