Why is the IMB blank but the job ended normally using MailStream Plus?

Product Feature: Parameters

Operating System: All platforms

IMBCTL O               W
IMBOUT 451 I                 C     083 Y   M

When the MailStream Plus 8.3.3 user’s First Class letter job has under 500 pieces, the job ends normally, but the IMB (Intelligent Mail® barcode) value is blank.  Why?
The job ends normally because of the W in position 24 of the IMBCTL parameter:
24 Process for Handling Invalid Intelligent Mail® Barcode Numbers - Define the handling of invalid Intelligent Mail® barcode numbers:
E Generate an error message and stop execution of the job.
W Generate a warning message in the execution log for each invalid Intelligent Mail® barcode. Continue processing and output all spaces for the invalid Intelligent Mail® barcode numbers.
blank - Default is E.
When using the W, the job ends normally as instructed.  With this warning for each record:
MSNA00A    I Invalid Outbound STID     at record # 000000001
The job’s execution log gives the error message for each record, but the job was told to give the message and keep going.
Then due to the STID value being invalid, the IMB will receive all spaces.

If the IMBCTL position 24 is changed to E -
MSNA00A    I Invalid Outbound STID     at record # 000000001
MSNA00A    E
MSDR01     I MSDR01 Ended abnormally. Processing terminated.
Then the job will end abnormally to alert you to the Invalid STID error message.
There is a new feature in MailStream Plus 8.3.3, IMBOUT position 40 with a Y:
Y Yes, allow a full-service STID to be used for non-automation mail.
But this is only allowed when the pieces are presorted and not Single piece rate:
Here is the USPS rule on this –
See page 12 section Full-Service Mailings in this document:

“ Full-Service Mailings
A mailer may use the same STIDs for the Full-Service and nonautomation portions of a Full-Service mailing, under
the following conditions:…..”

Single rate piece is not part of the Full-Service or Nonautomation portion, so that is why this functionality happens in MailStream Plus. 
For jobs that contain Single rate pieces, to avoid blank IMB values do not use the Y in position 40 of the IMBOUT parameter.  It is best to give the STID values in position 32 – 34 and 36 – 38 so the IMB will be created with the proper STID value.  For larger files (over 500 pieces in the Automation and Nonautomation presort groups) , the Y in position 40 to use the same STID value for both will work fine.
Please review the MailStream Plus 8.3.3 or later Reference guide to review the mentioned parameters for the full explanations.
UPDATED:  June 7, 2017