MailStream Plus on IBMi- why are some parameter's settings not found on the normal individual CHUI screens?

IBMi (iSeries, AS400) all versions
MailStream Plus (MSP) has many parameters and options for them.   On the IBMi platform, many are accessed on the main CHUI screens, via the below screen.  (This is the screen you are on after a job is selected.)

 16:19:17       MailStream Plus Presorting and Reporting System        UPCPDS00 
  2/16/2017           Replace with screen heading desired              UPCPDS01 
 Job @BVP@             Define and/or Submit a Presort Job              R08.3M03 

 Type options, press Enter. 
   2=Edit  6=Create 
                                      *-------- Last Activity ---------* 
   Opt  Function                      Date         Time       User 
 PX     Defaults for Print Output     09/16/2014   12:39:41   ABCD1234   
 PA     Mailing Piece Attributes      06/03/2014   17:33:25   ABCD1234   
 ST     Name/Address File Layout      08/17/2012   13:37:20   ABCD1234   
 PD     Presort Definition            09/16/2014   12:40:25   ABCD1234   
 NA     Name/Address Record Posting   08/17/2012   13:16:59   ABCD1234   
 M3     MAIL360                       06/04/2014   13:54:14   ABCD1234   
 RI     Information for USPS Reports  02/09/2017   18:13:30   ABCD1234   
 RR     Report Selection              02/09/2017   18:18:15   ABCD1234   

 SB     Submit Batch Job              02/10/2017   15:24:38   ABCD1234   

 F3=Exit   F12=PrevScrn    F20=View Parm File                     F23=Card Edit 

Parameters without individual CHUI screens are accessed thru the option in the lower right- "F23=Card Edit".  
That will take you to a screen where you can manually add and edit parameters that are not on the main screens.

More information about using F23, and a list of the parameters that are entered via F23, are in the MailStream Plus IBMi User's Guide for the version being used. Currently (MSP 8.3.3) the section is labelled "Additional Optional Parameter Processing"
Update Note:
Beginning with the MailStream Plus 8.3.5 release, there is no longer a separate IBMi User's Guide.  Now the information about using F23 Card Edit is in the main "MailStream Plus Guide" document, in a chapter currently called "Defining IBM® i Job Parameters".
UPDATED:  July 13, 2018