Non-migrated carriers will not send BM/CM “prime billings” through SIS (because they are obviously non-migrated in these transactions).
However, your other assumptions are not quite correct.
The following RAM rule is published in the RAM 2011 (was voted at RA44 Sep 2011):
Non-Migrated Carriers to respond via SIS
RAM A10 – Part 1:
If an airline receives a billing or rejection or correspondence that was submitted via SIS, and it wishes to dispute that billing, rejection or correspondence, it has to do so via SIS, therefore for such cases RAM Chapter A10 Part 2 applies.
Hence, if a migrated carrier rejects a non-migrated carrier, the non-migrated carrier need to respond via SIS (enter IS-WEB and create either RM or correspondence there).
Therefore, if during correspondence the “authority to bill” is given by the migrated carrier to the non-migrated carrier; the non-migrated carrier has to enter IS-WEB and create the BM there and link it to the correspondence.
As we know, non migrated carrier will not be raising BM/CM as they are not migrated to other transaction.
If a dispute between migrated and non migrated carrier reaches to correspondence and ultimately migrated carrier authorises non migrated carrier to bill migrated carrier to settle the correspondence, how non migrated carrier will raise BM.
Is there any provision in IS Web to raise BM to close the correspondence. Non Migrated carrier genrally raise invoice and not BM.