taxmap/instr2/i8839-009.htm#TXMP25249bb9
Line 13—Credit Carryforward(p7)

You must attach the appropriate documentation required, listed beginning on page 4 of these instructions, to support your claim for a credit carryforward. If you did not previously file Form 8839, you must amend your prior years' income tax returns. See Carryforward From Prior Years (2005–2009) on page 3.