I don't know of a easy way to do that through GDL, as each object would need to write its ID out to a text file or something in order to have the objects check each other. However a far easier solution would be to set up a schedule to list out all of the objects, their IDs and quantity. Then the users just need to check the list occasionally to make sure all IDs are unique.
Lachlan Green | Architect | Drafter
AC23 & 25 | Windows 10 | Intel 11Gen Core i7 | 2.5GHz | 32GB RAM | Nvidia T1200