Note that indexing GitLab data in Perceval does not index email addresses, probably because that's non-public PII which would require auth and specific permissions before being able to pull via the GitLab API would require auth, so what we get is only a random username:

"1234567890abcdef1234567890abcdef12345678": {
    "enrollments": [],
    "identities": [
        {
            "email": null,
            "id": "1234567890abcdef1234567890abcdef12345678",
            "name": "SomeName",
            "source": "gitlab",
            "username": "someusername",
            "uuid": "1234567890abcdef1234567890abcdef12345678"
        }
    ]
}

That means in contrast to Gerrit there is nothing that would allow identifying staff or non-volunteer GitLab accounts, as we only have a random username.

This will mean that our affiliation stats will become more incorrect.

DB query to list accounts not marked as affiliated is SELECT CONCAT("https://wikimedia.biterg.io/identities/hatstall/", uuid), name, username, source FROM identities WHERE source = "gitlab" AND uuid NOT IN (SELECT uuid FROM enrollments) ORDER BY uuid; but as written in the previous comment this isn't much of a help.
https://www.mediawiki.org/w/index.php?title=User%3AAKlapper_%28WMF%29%2FBitergia_data_quality_queries&type=revision&diff=5181316&oldid=5061622