Can I use the same record ID in two different arms in the same project?

Yes, but you must first disable auto-number for records which requires the first instrument to NOT be a Survey:

Then, add a new record using the Add / Edit Record, Record Status Dashboard, or Importing Data. If using Add / Edit Records, select the arm in the dropdown to select the arm to enter a new record then enter the Record ID.

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If the record ID exists on another page, there will be a warning at the top of the Record Home Page:

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