On the Vendor/Office Settings page, there is a setting for "Send all adjustment comments to vendor".
This setting was created to resolve a problem with CSM in which only the final Adjustment Reason and Comment would show up in Collaborati. (SUPPORTPRI-4344)
If the setting is OFF, then only the most recent comment is shared (if there are multiple comments, the older comments are not shared).
If the setting is ON, then all the comments are shared.
Notes from Engineering
We named the setting: "Send all adjustment comments to vendor" because we actually send both the invoice header adjustment comments and the line item adjustment comments.
Also the comments at the line item level which include the comments from the propagated header adjustment and the ones done directly on the line item will be displayed in Collaborati based on the Adjusted On date (no grouping will be done).
See more information here regarding Comments to the requestor