Before rebuilding in June 1958.
This loco was at 73A Stewarts Lane from 1956 until 1958 when it was rebuilt and sent back there. Note it has the self-weighing tender received from 35014 when that was rebuilt in July 1956 and later passed on to 35024 when 35015 itself was rebuilt.
Therefore the date is between July 1956 and June 1958.