As far as I know, a wiki's logging table should include an entry with log_type = 'newusers' for each newly registered user (since the logging system was created, of course).
However, this is not the case for a small number of accounts. The problem appears to be ongoing as of Jul 2024.
The problem seems to exist across all wikis. As an example, here is the count of cases from the Chinese Wikipedia:
SELECT
LEFT(user_registration, 6) AS registration_month,
COUNT(*) AS users_with_no_logged_creation
FROM user
LEFT JOIN actor
ON user_id = actor_user
LEFT JOIN logging
ON
log_actor = actor_id
AND log_type = 'newusers'
WHERE
log_timestamp IS NULL
AND user_registration IS NOT NULL
GROUP BY
LEFT(user_registration, 6)| registration_month | users_with_no_logged_creation |
|---|---|
| 200601 | 1 |
| 200603 | 2 |
| 200604 | 5 |
| 200605 | 65 |
| 200606 | 64 |
| ... | ... |
| 202401 | 156 |
| 202402 | 99 |
| 202403 | 222 |
| 202404 | 126 |
| 202405 | 251 |
| 202406 | 215 |
| 202407 | 170 |
| (Total) | 48749 |
As another example, here is the count for Commons:
| registration_month | users_with_no_logged_creation |
|---|---|
| 200601 | 3 |
| 200602 | 1 |
| 200604 | 2 |
| 200605 | 15 |
| 200606 | 18 |
| ... | ... |
| 202403 | 207 |
| 202404 | 143 |
| 202405 | 180 |
| 202406 | 167 |
| 202407 | 123 |
| (Total) | 377349 |