The unload job was executed for the first time with these options: REMEMBR=YES, UNLOAD=ALL, and it produces the following message:
DBG73109I DSN 12:35:36 DATA COLLECTOR POSTED TO REMEMBER POSITION
It was executed again with these options: REMEMBR=YES, UNLOAD=NEW, and this message was produced:
DBG73109I DSN 12:52:08 DATA COLLECTOR POSTED TO REMEMBER POSITION
The generated reports for the two runs were identical with the same data. Why the same reports being produced?
Executing the unload the unload process manually caused the problem. Executing the unload process automatically using the offload percent parameter resolved the problem.