I have met several people saying if you are 60% disabled or more you can file an amendment (1040X).
I have met one person that already recieved payment. You must include with each Form 1040X a copy of the official VA determination letter granting the retroactive benefit. I got text two letters needed to be added and va retro and other look like cost analysis, but darn pics are blurring. I will do amendments when verify two letters needed. Good Luck.
Example 19.
You retired in 2012 and receive a pension based on your years of service. On August 3, 2018, you receive a determination of service-connected disability retroactive to 2012. Generally, you could claim a refund for the taxes paid on your pension for 2015, 2016, and 2017. However, under the special limitation period, you can also file a claim for 2014 as long as you file the claim by August 3, 2019. You can't file a claim for 2012 and 2013 because those tax years began more than 5 years before the determination.
