Understanding Apple's per-ID 10-device limit

I am confused about Apple's 10-device-per-Apple-ID limit.

I am an Apple fanatic who owns tons of Apple devices, past and present, and uses nearly all of them on different occasions for different purposes. For example I have: my iPhone 6S, my iPhone 6 (used for app development and testing), an iPhone 5S (also for testing on smaller screens), an iPad mini, an iPad pro, a new 2015 MacBook, a MacBook Air (a dedicated work machine), an older 2011 MacBook Air (used specifically for app development also), a Mac mini (being used as an HTPC), an iMac, an older Mac Pro (using it as a server), and a 2007 MacBook (for testing things on older OS'es i.e. Lion). I'm also sharing my Apple ID with a close family member who has two devices - an iPhone and an iPad. This totals 14 devices, 7 of each type, all of which are actively used. Even if you forget about the family member I'm sharing with, we're still at 12 devices.

What isn't making sense to me is what exactly triggers a device to get added to this 10-device limit. Apple's documentation says "automatic downloads" or "downloading previously-purchased content including books, music, movies and apps" but this doesn't seem consistent. Example: my brand new iPad Pro will not login to Apple Music, saying that I've reached the limit of 10 devices. However, it will download apps from the App Store that I've previously purchased.

Also, I am unable to remove any devices from the list in the iTunes in the Cloud section. They all have their remove buttons greyed out. I don't mind if some of my older machines can't access Apple Music or even if they can't access every paid app, but I do use free App Store sourced apps on every machine (e.g. TextWrangler on Macs, Dropbox on iOS).

To further confuse me, I've never had to be conscious in the past about "deauthorizing" devices when it comes to apps. Over the past couple years I've easily had 20+ devices on my account at different times (all my own devices, but I upgrade a lot). Each of these devices has logged into my iCloud and downloaded apps from my purchased apps list. At no time was I ever made to specifically deauthorize any device in order to download my apps onto a new device. (iTunes Store content, i.e. music, movies, TV shows, has always had the 5-device limit - this isn't what I'm worried about. I'm mostly worried about apps.) Seeing this error with Apple Music on my iPad is the first time I've come across any issues with authorizing and deauthorizing devices.

Could someone help explain:

• What triggers a device to get added to the 10-device limit? Does it happen anytime you login to the App Store and/or iTunes Music store on any device? It doesn't seem to be the case because I have paid and free apps running on plenty of devices.
• How can I remove a device from the iTunes in the Cloud Devices page?
• What will removing a device from this section do? e.g. Will that device no longer be able to download app updates (even for free apps)? Will it be unable to download purchased apps? Will it be unable to play protected purchased content (iOS devices)?
• How has it been possible for me to associate clearly more than 10 devices in the past few years to my account without triggering this problem, but now I suddenly cannot stream Apple Music on my new iPad but can download apps to it?

The biggest concern I have honestly is apps. I have no problem managing and limiting authorizations to Apple Music, but I do need to be able to download at the very least my free apps to all my devices.

EDIT:

To quote Apple:

When you use certain iTunes Store features on your iPhone, iPad, iPod touch, or computer, your iOS device or computer is automatically associated with your Apple ID in iTunes account settings. These features include:

* Turning on iCloud Music Library.
* Downloading past purchases you made in the iTunes Store, App Store, iBooks Store, or Mac App Store.
* Turning on Automatic Downloads.
* Turning on Family Sharing.
* Subscribing to iTunes Match.

This suggests that there is actually a 10-device limit overall on how many devices I can have using apps I've purchased on my account. But this is clearly not the case - as per my list above I already have more than 10 devices on my account and it seems to be working just fine.

The only thing that seems to have triggered this situation is trying to play Apple Music on my new machine.

So, now the question becomes: is Apple Music using an authorization, or a device association, or both? Also, if device associations are supposed to be limited to 10 devices, how have I easily been able to have more than that many iOS devices pulling apps from my account over the years without ever manually disassociating devices?

If we go back to when I got my first iOS device, I could easily say I've had probably 20+ devices that have at some point had apps from my account installed on them. Most of those devices are old ones that I've sold or given away, but many I still have an use, albeit very infrequently - but never before have I ever run up against a warning about this when downloading apps on my account on a new device. The confusion for me is that I received the error when I tried to play Apple Music on a new device, not install apps on it - but I've never seen the error through the years and years of installing iOS apps on multiple devices - so I'm confused as to what limit I've actually reached and why.

Apple, seriously...why can't this just be SIMPLE? Apple Music should go alongside Authorizations. If there is some kind of limit on iOS devices and apps on them, then that should be device registrations (which I've actually never experienced). Keep it separate.

Solution 1:

It's all detailed in the Apple Support Article: View and remove associated devices in iTunes:

When you use certain iTunes Store features on your iPhone, iPad, iPod touch, or computer, your iOS device or computer is automatically associated with your Apple ID in iTunes account settings.

and

You don't need to associate your devices to buy content, download new purchases, or to play back content that you've saved to listen to offline.

To remove a device:

Under the iTunes in the Cloud section, click Manage Devices. Click Remove next to the device that you want to remove.

Note that only computers are Authorized and Deauthorized, and are limited to 5 per account. See this other article: Deauthorize your computer using iTunes

Finally, this Discussion gave a good answer on Authorized vs Associated:

A computer can be AUTHORIZED to play/use content purchsed from multiple iTunes Accounts. There is a limit to the number of computers that can be AUTHORIZED per account (5 total) but no limit as to how many accounts a computer can be AUTHORIZED to play. Once you have AUTHORIZED all the accounts AND downloaded all the purchased content from each account to a computer, this content can be also be played on any device ASSOCIATED with the computer. A device can only be ASSOCIATED to one computer but one computer can have many devices ASSOCIATED to it. As an example, you can use apps purchased on from multiple iTunes accounts on an iPad as long as the computer the iPad is ASSOCIATED with is AUTHORIZED to use/play the content for each of the accounts. Another example: if you also purchased music from all the iTunes accounts, you could listen to it on an iPad, iPhone and iPod as long as all three were ASSOCIATED with the computer where all the accounts were AUTHORIZED.

Solution 2:

Yes, I recently hit this with my AppleTVs, but it's not clear if downloading apps broke it or if you have to download content (TV/movies) for it to happen. I just had a long conversation with support over the weekend where they coached me to attach some of my aTVs to another AppleID that is in my Family Sharing plan. That will probably work, but with 2 factor authentication makes it unhandy for me to administer these devices.