Texts maintained in CMIR will be over written at transaction level-for this you need to activate "read info record" at VOV8 for this SO type..
Always texts will be overwritten by your configs also- from transaction to transaction(means from Sales order to delivery or delivery to Billing)-observe Text ID access sequence column Reference/Duplicate.
Please check these & confirm.
Further Normally standard system will throw the below error for CMIR related text object maintenance from KNMT.
Can you please tell us what you have done to process it further.
Phanikumar