No, Authorized computers and Associated Devices are two different things.
Authorized computers are those computers that you have signed your Apple ID into iTunes with, and then Authorized for your Apple ID via iTunes. Only computers are Authorized.
Associated devices are both iDevices and computers that you have done any of the activities on that were listed above. So, with your Associated Devices list, since you don't use Family Sharing, iTunes Match, Apple Music, or Automatic Downloads, that means that on the eight devices and the two computers showing, you have signed your ID into the iTunes Store, App Store, or both, and have downloaded past purchases using that ID to those 2 computers and 8 devices. You can find out how long each of those have left on the 90 day period by going to your Account in iTunes on one of your computers, click on "Manage Devices" under iTunes in the Cloud. You will see when the device or computer was associated.
For the Authorizations, you can only "Deauthorize All" once a year. If, on your iTunes Account, it is showing that "5 computers are authorized to play content purchased with this Apple ID" under the Account Summary section, then all 5 of your Macs are already authorized for your Apple ID. You wouldn't need to Deauthorize them.
Authorized Computers and Associated Devices are two entirely separate functions.
Computers Authorized to your Apple ID allows you to play content on your Macs in iTunes that were purchased with your Apple ID.
Devices Associated with your Apple ID allows you to download past purchases to the Associated Computer or device when it is signed into the iTunes Store, App Store (or on a device both) with your Apple ID. (and, also allows you to use the other services discussed for that Apple ID for those Associated Computers or Devices).
And again, you can find the detail of when the 90 day period would be up on the Associated Devices by clicking on the Manage Devices in your iTunes account. When you purchase your new iPad Pro, you will want to remove one of the devices on your list in order to add the Pro. Just remove one that you think you won't be needing to download any past purchases to.
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