MDAC 2.5 SDK - ODBC Programmer's Reference
Appendix G: Driver Guidelines for Backward Compatibility
In ODBC 2.x, loading by ordinal could be performed to improve the performance of the connection process. An ODBC 2.x driver exports a dummy function with the ordinal 199; when the Driver Manager detects it, it resolves the addresses of the ODBC functions by ordinal, not by name. This functionality is still supported for ODBC 2.x drivers but is not supported for ODBC 3.x drivers.