First, you should determine whether or not the legal are deductible.  In my opinion, many people assume, incorrectly, that all legal expenses incurred during the administration of a trust/estate are deductible.  They're not.  IRS’s Notice 2018-61 reiterates that an estate or trust may deduct expenses incurred in the administration of an estate or trust, as long as they would not otherwise be incurred if the property were not held in such estate or trust. 

If the legal expenses are deductible, then expenses incurred in years prior to the final return are lost.