My reading is that "finish" means doing Coordinate, leaving off the first part of this call.
Callerlab's definition seems to say that the first part of Coordinate is Single File Circulate once and a half. If this were left off, the subsquent part of the call where the "Center 6 Trade' could not be completed from a column.
Therefore the call is not valid from a Column.
At Challenge, the first part of Coordinate is a Circulate.
Coordinate:
This usage derives from the C2 concept of 'anything Coordinate'.
