Within ShareGate, if you do not provide an explicit mapping for an user, ShareGate will try to resolve the user automatically by using a decision tree as described here:
https://migration-tool.sharegate.com/hc/en-us/articles/360032616471
When it does not find an automatic map, it will copy the metadata over (i.e. John Smit created the file.

It is however nog possible to disable this automatic mapping. Whenever users leave the company and no longer exist within AD, you want to keep this metadata and as such, you should have the option to disable this search for the account and have the metadata copied directly.

The automatic mapping introduces a security risk, meaning that it might map John Smith (from Finance long ago) to John Smith (from manufacturing now active). This was, Jhn Smith from manufacturing who is a completely different person mikght suddenly get access to financial documents he should not have access to. As you cannot CONTROL this behavior, it imposes a direct security risk.

As such:

When no direct mapping is given:

• Make an option to automatically try to resolve the account or copy the metadata over directly
• When choosing for automatic mapping, provide options on which methods out of the 9 steps may be used to try to resolve the user.
• When choosing for metadata, skip automatic resolvement of the user.