In the very rare scenario that you have four digit Client Codes and, for some clients, these are the same number as certain years (such as 2019, 2020, 2021) there may be an issue matching these clients in the migration app.
This will only be an issue if the migration app is unable to exactly match on the Client Name and where the Client Code of another client happens to be a year that the migration would otherwise look for when matching on year (currently a number between 1999 and 2030). If the relevant year is in the migration source path, the migration app performs a match on that level in the source path. If this matches to a Client Code this results in the client's documents being matched to an incorrect client.
For example, there is a client that does not match on the Client Name but has documents in the year 2019. There is a another client with the Client Code of 2019. The documents for the client that could not be matched on the Name will match with the client that holds the Client Code of 2019.