System files will bring over any changes to user and role maintenance, along with a number of other system files.  How long has it been since you migrated the system files the first time?

I'm ok with not migrating the system files since not much time has passed. However, Sage support indicated that the system files will always have to be migrated regardless when you're upgrading from v2016 to v2021 and I've never heard that before. 

Never heard of that either.

Things that you generally need to account for with respect to system files. Naturally, other changes  in the system files might need to be accounted for - however, these are the ones I'm typically concerned with: 

1. Paperless office files 

2. User and Role Maintenance

3. UDF and Custom Panels ( newly added/changed  since initial migration )

How to re-migrate company data during upgrade

Above is Sage's official KB on re-migrating. Perhaps most notable: 

Migrate System Files: the first time you migrate, System files will automatically be migrated. During re-migration, you will be given the option to re-migrate system files. This will pull over all of the data from MAS_SYSTEM. This is not necessary during re-migration unless you want to re-migrate (replace) the System files.

Thanks Wayne. Great info to share! They gave me the impression that specifically for v2016 a re-migiration would be recommended due to version being so old. Appreciate the responses.

The only time I am aware of being forced to redo the system migration is if CRM integration is enabled.

Edit: my habit is to remigrate the system, just in case someone edited a UDF / user changed a password.  My only exception is if there has been significant work on the target system (like updating a bunch of paths for Paperless / VI jobs, Role updates...).

I have a question about system files again. I have a v2022 install and want to migrate a company from a completely separate v2019 install into it. During migration, it did not give me a choice and said system files will be migrated; however I do not want to write over the v2022 system files.  

Situation is the v2022 company bought out the v2019 company and want to add them to their install. I would like udfs to come over but not the the users, etc.

Not sure the best way to accomplish this. It's not best practice but I can drop the MAS_xxx in the v2022 in the mas90 directory, create the company code and upgrade the data to get around this. But I can't import the udfs due to not being the same version.

You don't migrate, you copy the company data into the new system... but you're going to have a real problem with that, because of the new encryption keys.  Open a case with Sage for their assistance.

For the UDF's, do that manually (add to the new system, normally, before copying in the external company data... and you'll have to add the new system's UDF's to the source company data too).  Beware the custom office import... I've had that irreparably corrupt a system where we had to restore from backup.  Take backups at every step.  Seriously, every step.

Thank you. Great advice from your experience. Appreciate it!

Thank you. Great advice from your experience. Appreciate it!