When you start the 12.5.4 server, the new system types are installed in systypes. If you returned to 12.5.0.3:
The new types remain in systypes, but server operation is not affected provided you did not use the new types on the 12.5.4 server
You cannot create using date or time because error checks were added
If the server encounters date/time tokens, it raises error messages
If the server encounters a 12.5.4 procedure that accesses a table with date/time types, a stack trace results.
If you returned to a pre-12.5.0.3 server, nothing prevents you from creating objects using date and time types (since no error handling code exists for this purpose), but this is not advisable because any operations on those objects such as selects or inserts result in stack traces.
If you have created 12.5.4 tables with date or time columns, or procedures with date or time parameters, you need to remove references to these types before rolling back to a pre-12.5.4 server. You can run the following, which identifies the offending tables and procedures, advising you to remove references to them or use alter table to modify the types:
sp_date_time_type
If sp_date_time_types does not find any date/time objects, it marks procedural objects for recompile, removing all internal references to these new types
