you did something wrong in 2018 since you say you totally liquidated your position.  in the 2018 k-1 there was a box to check final k-1 a second box about the type of disposition and a link (quickzoom) where certain sales info needed to be entered.   not knowing all the details of the partnership (is it a publicly-traded one there would be a box checked on the actual k-1).     then you would need the supplemental schedule provided to enter the correct cost basis and any ordinary income upon sale.    tt is correct in that the sale gets entered on the 8949 but cost basis needs to be corrected.  in the sales section of the K-1 despite what tt says the ordinary income portion is entered as the sales price basis is 0 and ordinary income again is the sales price.  this flows to form 4797 line 10.  not every PTP has ordinary income recapture (then enter $0 for sales price and ordinary income)  however, the cost basis reported on the 1099-B needs to be corrected.  you will need to amend your 2018 return.  that is the year the unallowed losses should be allowed (I'm assuming you had basis to deduct these losses)