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All RTL routines were designed to be backwards compatible with the old VMS version. So, programs that follow the old RTL interface rules will continue to work on VMS. This includes no need for a terminator, use of optional arguments, calling the Fortran routines from C, and even the inclusion of arguments that have been removed in the new version.
While the old ways still work, they work only under VMS. Any program that does not follow the new rules for calling the RTL will not work on any other machine. This may cause problems for people trying to develop portable code under VMS, until they fully understand the new rules, because an invalid program will work under VMS. The way around this is to try the program frequently on a Unix-based machine to make sure you are writing truly portable code.