research@x1-analytics-slave [enwiki]>
SELECT notification_timestamp, event_type
FROM echo_notification
JOIN echo_event ON event_id=notification_event
WHERE notification_timestamp = notification_read_timestamp;returns 2653 rows.
with
where notification_timestamp != notification_read_timestamp;
Returns 7958893 rows
The amount of notifications where sent time == read time is only 0.03%.
I think it's plausible they're not in error: that the moment they're sent, they're already being read (by accidentally visiting the target page at that exact time, or marking "read all" at that exact time)
87% of those notifications are "edit-user-talk". If I'm not mistaken, those are automatically marked as read when visiting the talk page. I suppose pretty likely people hitting refresh a couple of times when they're engaged in a conversation they're awaiting response for.