I did not report unrealized losses from K-1 for ETF I held for last 3+ years. Now, that I sold shares, my last K-1 shows I have gains while I have losses.

[mgrab]

I sold shares of ETF I bought in 3+ years ago. I never reported anything from their K-1s, as I thought the profits/losses over those years are unrealized. Now, my last K-1 shows profits while I have overall losses.

Is there anything I can do to correct my mistakes i.e. to re-claim losses from, ideally all, previous years?

[DianeC958]

You could go back an amend the tax returns for the prior years, but that may not be the best option since any return prior to 2016 (until April 15, 2020) are beyond the statue to receive any refund possible. 

Also once you file a return with the IRS the statute of limitations begins, if you file an amended return the statute stars over once the IRS processes the amended return.

Depending on the size of the losses it is important to weight the possible tax liability with the additional time and work to amend the prior returns.