When we prepare to upload an attachment file to SharePoint somewhere, we will check whether there is same name file under the same position. And then if yes, compare the MD5 values for both contents. And if MD5 value is different, we will add unique suffix for the new attachment file(by current time ticks) and upload it to SharePoint.
So if the attachments in different Notes docs are identical, we just keep one under same position after migration.
The key is MD5 value from file content.
If one attachment in different Notes docs is different for content with same name, We would keep them depend on order of migration.
For example:
Doc1: attach1, attach2
Doc2: attach1, attach2(md5 different), attach3
Doc3: attach1(md5 different), attach3
If the doc3 is first to upload to SP, there are attach1(map doc3), attach1_xxxx(map doc2), attach1_xxx(map doc1) under the attachment folder.
If the doc1 is first to upload to SP, there are attach1(map doc1 & map doc2), attach1_xxxx(map doc3).
Please note the checking purpose is for decreasing the duplicated file. However, it can't prevent the duplication entirely.
