Taxpayer, fiduciary, designee: how official tax forms model who is acting (Formspedia Digest #1)

Formspedia — Sat, 31 Oct 2026 20:42:32 +0000

If you build anything that fills, validates or stores government forms, sooner or later you hit a form where the person signing is not the taxpayer. These forms are a useful case study in data modelling, because the agencies have already worked out which identities have to be kept apart.

This month's Formspedia digest looks at five of them. Below are the patterns we noticed while writing the guides, with links to each one.

1. Two identities, two fields, two ID types

Alabama's FDT-V payment voucher for estates and trusts has a "legal name" field for the entity and a separate field for the fiduciary's name and title. The only identifier it asks for is the entity's FEIN. The fiduciary's own SSN never appears.

Modelling note: the person filling the form is not the subject of the form. If your schema has one name and one tax_id, this voucher breaks it.

2. One person, two subjects, two records

IRS Form 56 notifies the IRS of a fiduciary relationship. The instructions require one notice per taxpayer represented, and they treat a decedent and the decedent's estate as two taxpayers. So one executor can produce two Form 56 filings: one keyed to the decedent's SSN or ITIN, one keyed to the estate's EIN.

Modelling note: the relationship is (fiduciary, taxpayer), not a property of the fiduciary.

3. Wildcards are rejected

Form 8821 authorises disclosure of tax information. Line 3 needs an explicit tax type, form number and period. The instructions say "All years", "All periods" or "All taxes" will cause the form to be returned. Periods use a YYYYMM style, and fiscal years use the ending year and month. For estate tax matters the period field holds the date of death instead.

There is also a sentinel value: a designee without a CAF number gets the literal string NONE.

Modelling note: validate for explicit enumerations and reject wildcard text before the PDF is generated, not after the IRS mails it back.

4. A single-choice field that decides the attachments

Nebraska Form 1310N (refund for a deceased taxpayer) has three boxes in Part I and the claimant checks exactly one. Each box implies different evidence: a joint-name check for box A, a court certificate for box B, proof of death plus Parts II and III for box C. A "yes" on line 2 of Part II invalidates a box C claim entirely.

Modelling note: this is a discriminated union. The box value should drive which attachment and section validators run.

5. Totals that flow into another form

HMRC's IHT406 collects bank and savings balances for an estate. Box 1 flows to IHT400 box 52, and box 5 (the sum of boxes 2, 3 and 4) flows to IHT400 box 54. Each amount is capital plus interest due but unpaid at the date of death.

Modelling note: cross-form references belong in the data model as explicit mappings, so a change to the parent form's box numbers can be found in one place.

All five guides link to the official PDF and instructions they are based on. The full library by country is at formspedia.com/us and formspedia.com/uk.