IRS Statistics of Income estate-tax data come from Form 706 returns. The IRS explains that gross estate can include real estate, cash, securities, businesses, and decedent-owned life insurance, with deductions applied to calculate the taxable estate. That definition is broader than a property-record search and narrower than all estates.
Filing year is not death year
The IRS filing-year tables describe returns filed during a calendar year. Because returns can be filed after death, the filing year may include decedents who died in several years. The IRS filing-year tables state this directly and should be cited whenever a table is used.
Use the metadata before the number
Log the table name, filing year, classification, units, source workbook, access date, and any footnotes. Do not call a Form 706 count a probate count or use an aggregate gross-estate category as a valuation for one parcel. Move to the return, court, deed, and tax records for matter-level evidence.
Professional disclaimer: General research only, not IRS, legal, tax, appraisal, or fiduciary advice.