Migrating to C-ISAM 4.10

I have recently received the latest version of C-ISAM - 4.10 Having flitted throught the associated documentation, it seems to me that the major enhancement is support for variable length records (VAR). Informix's implementation of VARs has produced changes in the structure of index nodes (.idx) and data (.dat) files (as well as others). A magic number, stored within the index file is used to check the validity of a C-ISAM file. However, this magic number has not changed between 4.00 and 4.10. Does this mean that C-ISAM 4.10 cannot distinguish between pre 4.10 files and current ones ? If so, does this mean that every pre 4.10 C-ISAM file needs to go through a manual conversion process - surely not? Your comments please .... Regards,