A user changed all timestamps by one year on a page I'm subscribed to (not watching): https://www.mediawiki.org/w/index.php?title=Talk:Edit_check&oldid=prev&diff=6381816
This generated notifications for the 23 topics on that page:
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We could probably be more vandalism resistant by limiting the number of new topics we detect per edit. Although there may be legitimate case where this happens, e.g. a handful of discussions being moved to a more relevant page.
It just depends which edge case you want to design for...