When did the ability to create/edit Core UI reports become deprecated.

We have known for a while that Core UI reports would be deprecated in favor of Platform Analytics.  We've planned for such in that our baseline reports we created as part of our product were migrated over to Platform Analytics.  However, we have noticed that even on Xanadu Patch9, we cannot create new or update existing Core UI reports.  We can run existing ones - just not edit them nor create new ones.  My question to the community is the following.  In what release was this "quietly" disabled?  Are there any release notes to such?  It isn't a full deprecation of Core UI reports but a soft deprecation.  

Thanks in advance.