Unfortunately there’s no way I’m aware of to get that data retroactively. @Bastien_Siebman or @lpb, do you guys have any ideas?
But I have another note of caution for you: be aware that the story data you’re retrieving is not a complete and total record of changes to the tasks. See this post for more. Because what’s mostly lost are multiple events within a 24 hour period, the missing data may be less significant for your purposes; I could be wrong but I’m thinking most updates to due dates don’t occur more than once within 24 hours. But I wanted you to be aware of the missing-data issue.