Yes! Terra supports historical data retrieval via the REST API. You can call GET /v2/activity, /v2/daily, /v2/body, or /v2/sleep with start_date and end_date parameters to backfill data from before the user connected. Requests spanning more than 28 days are treated as "large requests" and processed asynchronously, the data gets sent to your webhook in chunks.
This is one of the advantages of using Terra API, see our docs: https://docs.tryterra.co/reference/get-activity-data
Hope this helps!