Here you find a brief explanation of what happens when a Media Campaign gets changed or cancelled:
If your Credit Note Media Campaign has not been fully invoiced but only partially for a certain time period (i.e. monthly: January) and you change something (6.4 Cancellations & Credit Notes / 4.11 Optimizer), then these changes get added to the open Credit Note Item (i.e for February). If there are no open Credit Notes (i.e. you've invoiced all Credit Note Media Campaigns which were expected) then a correction Credit Note Campaign will be created for that Publisher Payout Contract.
(Version 2.107 and lower) If all Credit Notes for your Publisher Payout are invoiced - any changes will be lost and not considered in a new credit note.
(Version 2.108 and up) If all Credit Notes for your Publisher Payout are invoiced - any changes will be considered in a new credit note as a correction. You will recognize these campaigns by:
the sequence number which will be written into the field Publisher Payout Correction Sequence in the Credit Note Media Campaign
postfix of the sequence number which will be added to the Media Campaign Name.