You take the credit as of the date when the property is installed (placed in service).
So a credit for doors and windows installed in 2014 can only be claimed by filing an amended return for 2014.
Also, be aware that the credit for doors and windows is 10% of materials only; installation is not eligible. The maximum credit is $300, and the maximum lifetime credit for all residential energy efficiency improvements is $500. Doors and windows must meet Energy Star version 6.0 requirements, not all do. Check with your manufacturer.
The deadline to file an amended return for 2014 to get an additional refund is April 15, 2018 (about one month from now).
