I have this problem too often.
My message should indicate 6 installs for my purposes.
OSX 10.9 to 10.12 on two computers.
For those who also do this you should be aware that you "can" do this on one hard disk with multiple partitions but you will have user domain problems. (duplicate and triplicate "open with" issues)
Software Update (App Store updates) can also be quite confused unless you place each version of OSX on a separate hard drive and Do Not have them mounted internally.
To repeat, you can do this the easy way but there will be some sneaky troubles unless you know the Terminal Commands to get rid of "duplicate open with".
Best method is to buy some extra Mac Pro drive sleds for swap and store each version of OSX externally OR, have the drives in an external enclosure.
I operate OSX 10.4 to 10.12 using this method.
"Moving to Adobe Creative Cloud" is a non-sequitur response. (entirely nebulous)
I am seeking to acquire knowledge BEFORE I attempt to upgrade my CS6 MC software.
"MOST" online activated software does not check the computer ID, it only counts the number of installs.
IF.... the installer actually checked the computer ID, IF..., it would verify that that the software is being installed on the exact same computer multiple times. (multiple versions of OSX)
Most Apple users effectively trash their previous version of OSX because they use only one internal hard drive for boot.
Mac Pro Tower users can use up to 10 internal (separate) physical hard drives.
Wisdom dictates that the previous version of OSX be archived because Apple does not provide the ability to revert to previous OSX version.
This reversion inability can and does cause all sorts of problems including installed application incompatibility.
Those of us who use the computers for "computing" rather than internet surfing and social site nonsense cannot allow these problems to occur. (all work would stop)
Thus... fully operational versions of previous OSX MUST be created and maintained prior to installing the next version.
The final result is, "most" online activated software and installers become a problem due to lack of sophistication.
(installer does not check computer ID)
This prevents installation of the software on MULTIPLE VERSIONS OF OSX ON ONE COMPUTER.
(installer "ASSUMES" that the computer has only one hard drive and consequently one version of OSX)
The details of incompatibility issues and lack of capabilities associated with each new version of OSX is extensive.
In short... each new "upgrade" since Snow Leopard has decreased capabilities, especially utilities and file / folder / Finder operations while providing a small handful of new Internet related capabilities not required for professional purposes.
Splitting hairs is a waste of time.
The summary is... I need to install CC applications on two computers with multiple versions of OSX without being charged for 6 subscriptions. (two computers as defined by the SLA and in fact, only two computers)
IF... I could contact Adobe directly I could solve this problem as I have done with other online activated software installs.
PERHAPS????.... the Adobe installer is sophisticated enough that this is not a problem?... I don't know.
What I do know is that I do not want to be charged $120 a month for two computers.