you don't say what's on line 10 which is the total capital gain nor what the 754 adjustment would have been. it would have been the fair market value of all the partnership assets less liabilities less their tax basis times the descendant's ownership interest.
in part the line 9c amount will be offset by the capital loss on disposition
assuming no other capital gains or losses if line 10 were 200 then the 190 loss would reduce the overall gain to $10 and only the 10 would be recaptured as 1250 gain, if line 10 were 300 then the overall gain would be $110 all taxed as 1250 gain
if 754 had been elected then line 10 would go down by the 754 step up but up by the additional depreciation that would have been taken on the 754 adjustment and post death depreciation, so line 9c would be higher than the $10.
to give an example, the depreciable portion of the property seems to have been almost fully depreciated so assume it was since it was a 27-year-old business back in 2014. if the land was valued at 292 the building would have been valued at 1208. 1/8 pf that would be 151. on that an additional ~5.50 in depreciation would have been taken each full year (151/27.5) since it was about 8 years between death and the sale the maximum amount subject to 1250 recapture would have been about 44. now say the property was sold for a net of 2000. 1/8 of that is 250. so gain = 250 (sales price) - 151(tax basis building including step-up) +44 (depreciation) - 36.5 (1/8 of the 292 in land). if my math is correct line 10 would be 106.5 and line 9c would be 44. also, to take into account is that each k-1 over the intervening years would report less profit due to the additional depreciation. whether the passive loss rules would come into play is unknown. still not as good if 754 had been elected.
maybe the accountant was unaware of 754 but then why didn't the executor raise the issue when the k-1's came out without it. there may have been a chance for a late 754 election.
This is my understanding of how the tax laws apply in your situation. I no longer actively prepare tax returns. You are free to consult with an outside tax lawyer or other tax pro to see if they can offer some sort of relief. I would warn against not reporting what is on the k-1's since this could generate a notice from the IRS and potentially result in substantial penalties.
