Disability Tax Credit--do I need to amend returns?

[F-bomb]

I expatriated in 2014 and did my final returns and 8854. In 2016 I was approved for the disability tax credit here in Canada, due to a lengthy illness. There is a retroactive component to the tax credit that includes years 2012, 2013 and 2014 when I was a US citizen. I have not put in for this retroactive amount yet because I am unsure if this means that I have to amend my US tax returns once my Canadian returns are amended to reflect this credit for previous years.
First off, I am not even sure how the credit is treated for US tax purposes. Secondly, I did read somewhere, but cannot confirm, that there is no requirement to amend previously filed US tax returns. Can anybody please advise?

[nelsona]

You would only need to amend your previous returns if you relied on the foreign tax to reduce your US tax, and this tax has now been reduced to the extent that you now owe US tax, or reduced the carryforward on 1116.