It seems that the editingSessionId field is regularly duplicated in wikitext edit sessions, but not VE sessions.
> SELECT -> event_editor, -> COUNT(*) AS sessions, -> SUM(revisions > 1) AS cross_revision, -> SUM(pages > 1) AS cross_page, -> SUM(users > 1) AS cross_user -> FROM ( -> SELECT -> event_editingSessionId, -> event_editor, -> COUNT(DISTINCT `event_page.revid`) AS revisions, -> COUNT(DISTINCT `event_page.id`) AS pages, -> COUNT(DISTINCT `event_user.id`) AS users -> FROM Edit_11448630 -> WHERE -> timestamp BETWEEN "20150401" AND "20150402" AND -> event_action = "saveSuccess" -> GROUP BY 1 -> ) AS session_counts -> GROUP BY 1; +--------------+----------+----------------+------------+------------+ | event_editor | sessions | cross_revision | cross_page | cross_user | +--------------+----------+----------------+------------+------------+ | visualeditor | 13416 | 0 | 0 | 0 | | wikitext | 309795 | 627 | 3 | 0 | +--------------+----------+----------------+------------+------------+ 2 rows in set (49.02 sec)
I did some more digging. See my notes here: https://meta.wikimedia.org/wiki/Research_talk:VisualEditor%27s_effect_on_newly_registered_editors/Work_log/2015-04-13
TL;DR: 100% of dupe sessions have only one "init" event.