You have a requirement to Update/Replace some data in Customer Master Data. You are using Replace already existing records but after successful migration, you could find those Accounts are created again in the system with different ID.
The cause for the issue is as follows,
1. Initially, you have set the Review Settings for Number Assignment for Customer IDs as New numbers taken by migration service. This was performed in Convert Values step when you execute the migration file.
2. When you did the Customer migration, the ID provided in the template was X due to above setting, system generated the new ID Y.
As per system behavior, if you want to make any changes (through migration) to the Account Y, then the Account ID which you need to provide in the template is X .
3. But the ID which you might have provided during replace was Y. Hence, the system generated the new ID Z.
In order to wipe a value, you can use Replace mode but the Account ID should be the initial ID which you used to add the Account Initially (X).
Note: How to find the Account ID mapping?
In the migration of Customers, select a Completed file, select You can Also and choose Export Value Conversion to File.
X - Account ID from Legacy system or the the Account ID which you used in the template while creation of the Account
Y - Account ID which was created by the system through migration
Z - Account ID which was created by the system when you used Replace mode.
This is expected system behavior.
For the duplicate Accounts, you need to change the status to obsolete
KBA , LOD-CRM-PRO , Products , How To