Polycom RMX 2000 Administrator's Manual page 238

Appendix C-CDR Fields - Unformatted File
C-2
The MCU sends the entire CDR file via API or HTTP, and the RMX 2000
or external application does the processing and sorting. The RMX 2000
ignores events that it does not recognize, that is, events written in a higher
version that do not exist in the current version. Therefore, to enable
compatibility between versions, instead of adding new fields to existing
events, new fields are added as separate events, so as not to affect the
events from older versions.This allows users with lower versions to
retrieve CDR files that were created in higher versions.