At least one survivor of a Valenwood purge agrees to help the Dragonborn break into the embassy because the Thalmor murdered his family... according to the Blades. Thalmor sources hint that it was the Blades that killed his family. Otherwise, there are no mention of these purges.
What is the source? I've never come across it, and it seems so unlike the Blades' to do something so underhanded to get a sympathetic contact. It's more the Thalmor's style.

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