"Hence, the final Schedule K-1 should show a net loss that accounts for my remaining capital account, but is short of that amount." not necessarily so. there are some possibilities. however, you can file an amended 2019 return and decide how to handle the remaining capital a/c balance - either as a capital loss or ordinary loss.
Since you are guessing as to how to handle the remaining a/c balance and thus your return might be inaccurate use form 8082, Notice of Inconsistent Treatment to identify estimated K-1 items or when you disagree with the amounts reported on the K-1. yours is a BBA partnership
unless the CFO is lying about his status, he no longer has the right to issue corrected tax forms. since it usually costs $'s to formally close an LLC with the state, it's quite common for nothing to be done. when the annual fees aren't paid or the annual filing isn't done for several years in a row, the state will automatically dissolve the LLC.
there is one other possibility about the balance in the capital a/c. and that is the amount is for non-deductible expenses that weren't properly reflected on the k-1's. that would leave you with a zero basis and thus no additional ordinary loss and no capital loss.
