@havinabubble wrote:
But why has ALL my guest OS suddenly changed to thinking they have been created on a newer version? (when they haven't).
A thought which occurred to me:
Where are your VMs stored on your daily driver iMac? In particular, are they stored in a folder which is being synced with a cloud service, such as Dropbox or iCloud Drive? iCloud Drive potentially includes the Desktop and Documents folders and everything under them, depending on whether that option is chosen in System Preferences > iCloud > iCloud Drive.
The unexpected upgrade of your VMs might be explained if they are being synced with another Mac running a newer version of VMware Fusion, and changes made on that newer version are being synced back to the Mac running the older version.
If I'm right, this is a very bad idea - apart from the risk of this sort of issue, VMs are inherently not safe to store in locations that are synced with cloud services, because the VM frequently modifies parts of files and needs to do coordinated changes to multiple files, which may not sync reliably, resulting in file corruption and/or a bad copy of the VM in the cloud (or other computers to which it is also synced). Another problem is that the cloud sync service might decide to evict some files from local storage if it thinks they aren't in active use, which could break the VM.
