Here RC refers to the Reporting Centre, i.e. the office where the application has been assigned to.
Eg:
RC-6262: CIO Centralized Intake Office in Sydney, Nova Scotia
RC-9245: OSC Operations Support Centre in Ottawa, Ontario
RC-6029: New Delhi
Etc.
The L number is the officer who assigned the application to the reporting centre.
The due date is the system generated date to remain the officer of the pending task or application. Due date does not have much significance as most application are processed way before it and others keep pending way past it.