What is true of any created custom attribute or object class?

While custom schema is often managed separately, the statement that it 'cannot be placed in one of the default distributed schema files' is not universally accurate, as specific implementations may allow integration or extension mechanisms.

While top-level OID arcs are registered with IANA, individual custom attribute or object class names do not require IANA registration; their OIDs must simply derive from a privately assigned OID branch.

Every custom attribute or object class defined in an LDAP schema must be assigned a globally unique Object Identifier (OID) to ensure that it is distinctly identified across all LDAP directories and avoids conflicts during replication or integration.

There is no general restriction preventing custom attribute or object class names from containing numbers, provided they adhere to other naming conventions.