Within the "Rebate Setup" page, you can choose to turn on the Combine Sales/Purchase Output Doc toggle. By default it is switched off, meaning any Document Output documents that are created are individual, usually by Rebate Card and then per allocations within in. 

However, there may be the instance you have multiple Rebate cards for the same Customer/Vendor and you wish to combine all of their rebates into just 1 document rather than multiple. This can be handled by changing the Combine Sales/Purchase Output Doc to 'Yes'. 

Regardless of whether you create the document output directly from the rebate card or from the Tell Me (search), when this is 'Yes', Business Central will check to see if there are other 'Active' Rebates for the same Customer or Vendor and pull all of the related rebate data into 1 Credit memo or Purchase Invoice. 

Where this is used, your Output Document will appear like below, displaying multiple Rebate No's, values and ensuring the total for the document output includes them all. This means that across multiple rebate cards, you may have rebate entries all linked to the same Issued Document where usually, these would be unique to the individual Rebate. When the output document is posted, reversal accrual postings are made as normal, checking all of the linked rebate entries and creating reversal entries for all that apply.