Unfortunately, the IRS is not concerned with the time period between the date-of-death and the sale of real estate acquired from a decedent unless that time period is very short and there was no chance of any significant appreciation.
An appraisal done several months after the date of death may be accepted (or, more likely, simply never be the subject of a review), but the IRS is only obligated to accept a date-of-death appraisal from a certified real estate appraiser.
