ASIEXP81 does get upgraded post GP 2016, ASIEXP83 doesn't get upgraded at all, ASIEXP86 last gets upgraded at the 14.00.0704 version and ASITAB20 doesn't get upgraded. These would be the main SmartList tables, though there are many others.
To understand, it sounds like all of the custom SmartList reports are missing but all the default SmartList folders and reports show correctly after the upgrade to GP 18.4?
If so, were the custom SmartLists created in SmartList Builder and is that product installed?
We haven't seen any issues with missing SmartLists post upgrade, whether default or custom, though if the custom reports were created via SLB and that isn't installed, that may be an issue.
This script will show what custom reports are present:
Select * from ASIEXP81 where ASI_Favorite_Type > 499 and ASI_Favorite_Type < 2000 order by ASI_Favorite_Dict_ID, ASI_Favorite_Type
Thanks