DOCUMENTATION OF MODEL ASSUMPTIONS - Complete Guide with Case Laws

Model Assumptions are the foundation of any financial, valuation, risk, or business model. If assumptions are not documented, the model has no defensibility in audit, regulatory review, or court.

1. WHAT IS MODEL ASSUMPTION DOCUMENTATION?

It is a structured record that explains:

Every assumption = What you assumed + Why you assumed + Source + Impact if it fails.

As per Federal Reserve SR 11-7 and RBI Model Risk Guidelines, a model is defined as having 3 components: Inputs, Processing, Outputs. Assumptions sit in all three. Failure to document them is considered Model Risk.

2. WHY DOCUMENTATION IS LEGALLY MANDATORY?

1. Audit Trail: Auditors under SA 540 / Ind AS 113 require you to justify fair value assumptions.
2. Regulatory: SEBI, RBI, SEC require you to show you understood your own model.
3. Litigation: Courts apply the Daubert Standard - expert testimony based on unsupported assumptions is inadmissible.

SEC Principle: "The failure to understand models employed by registrants may alone be sufficiently negligent that any resulting misstatement will be deemed negligent."

3. TYPES OF ASSUMPTIONS TO DOCUMENT

4. STANDARD DOCUMENTATION FRAMEWORK

For each assumption, document these 9 fields:

1. Assumption ID: MOD-ASS-001
2. Description: e.g., Terminal growth rate 3%
3. Category & Criticality: High / Medium / Low
4. Source & Rationale: Bloomberg, Management discussion, Historical average
5. Methodology: How it was derived
6. Alternative Considered & Rejected: Why not 5%?
7. Sensitivity: If assumption changes by +/- 1%, Valuation changes by X%
8. Owner & Approval: Who proposed, who approved
9. Validation Date & Limitation: Last reviewed, known weakness

Regulatory Oversight can have a profound impact on financial models

5. CASE LAWS - WHERE ASSUMPTIONS FAILED

This is the most critical part for legal defensibility.

CASE LAW 1: SEC Fines for Model Error - $3 Million Fine

Citation: SEC vs Investment Advisers using flawed quantitative models, Mayer Brown Analysis

An asset manager used a computer model with an error. The SEC held that the firm failed to understand its own model. Fine of $3 Million imposed. The order is a warning for firms using AI/ML where models may be opaque.

Learning: You must document model validation and have a person who understands the model. "Black Box" is not a defense.

CASE LAW 2: Columbia Pipeline Group v. Crow - Delaware Court of Chancery

Citation: In re Columbia Pipeline Group, Inc. Merger Litigation

The Delaware Court of Chancery rejected the petitioner expert's DCF analysis to determine fair value and explained why DCF is questioned when terminal value assumptions are flawed.

The court found the expert used an unrealistic perpetuity growth rate inconsistent with capex = depreciation assumptions.

Learning: Terminal value often 70-80% of DCF. If capex < depreciation forever, you cannot grow forever. Assumption must be internally consistent.

CASE LAW 3: DFC Global, Dell, and Aruba Networks Appraisal - Delaware

Citation: DFC Global Corp. v. Muirfield (2017), Dell Inc. v. Magnetar (2017), Verition v. Aruba Networks (2019)

Court rejected DCF valuations from both sides where one argued $32.57 and other $19.75 for Aruba and instead relied on Deal Price as fair value.

The Court also modified defendant's valuation based on assumptions about capital structure, cost savings.

Learning: When DCF assumptions are highly subjective and conflict, courts prefer market evidence. Document why your assumptions are better than market price.

CASE LAW 4: ITAT Jaipur - DCF vs NAV under Section 56(2)(viib)

Citation: ACIT vs. M/s [Private Company] - ITAT Jaipur - Addition of Rs. 18.57 Crore Deleted

The controversy: AO rejected merchant banker’s DCF valuation and substituted NAV method calling future projections unreasonable.

Tribunal held: AO Cannot Replace DCF Valuation with NAV Merely by Calling Future Projections Unreasonable. If DCF is done by prescribed method (Rule 11UA), AO must show specific flaw in assumptions, not just general doubt.

Learning: Documented assumptions by a Category I Merchant Banker have legal sanctity under Income Tax Act in India.

CASE LAW 5: Courts Dismiss Claims Based on Pure Assumptions

Citation: Ajay Singh (Sunny) Deol vs Suneel Darshan - 2015 Supreme (Bom) 543 & Bhagwandas vs Mohd.

Principle: In cases where no evidence of actual damage exists, awarding damages based solely on assumptions or hypothetical losses is contrary to legal principles.

Learning: In damages/loss of profit models, you cannot just assume loss. You must prove factual basis.

CASE LAW 6: Buyout Dispute - Unrealistic Projections Rejected

Citation: Business Valuation Resources - Court Discredits Valuation Based on Unrealistic Projections

In a buyout dispute, court rejects departing shareholder’s valuation where DCF model relied on company projections used for a bank loan that were never realized and were “not accurate”.

Learning: Bank loan projections are optimistic by nature. You cannot use them for fair valuation without normalizing. Document the purpose of projections.

CASE LAW 7: Daubert Challenge - Expert Testimony Struck

Citation: Business Valuation Resources - Testimony of damages expert excluded due to no basis

Opposing counsel filed Daubert motion claiming expert's pricing calculations had no factual basis. After testimony, court struck it because assumptions “had no factual basis in the trial evidence.”

Learning: The court allowed testimony initially as long as there is a basis for assumptions in the record. If later you fail to connect assumptions to evidence, entire report is struck.

CASE LAW 8: Australian Case - Importance of Instructions to Experts

Citation: Mondaq Australia - Importance of appropriate assumptions

Expert evidence was rejected by the court because it was based on assumptions that were unsupported by a reasonable basis.

Learning: The instructing lawyer must give correct assumptions. If expert builds model on wrong legal assumptions, model is worthless.

6. DOCUMENTATION TEMPLATE YOU CAN USE

Model Name: [e.g., Startup DCF Valuation - XYZ Pvt Ltd]
Purpose: Fundraising under Sec 56(2)(viib)
Model Owner:...

Assumption Log:

Revenue Growth: 18% YoY for 5 years. Source: Management business plan, validated against NASSCOM industry growth 15-20%. Sensitivity: -5% growth = Valuation -22%. Limitation: Historical data pre-COVID world - models designed in pre-COVID world failed.

WACC: 14.5%. Rf 7.1% (10Y G-Sec), Beta 1.2 (comparable), ERP 6%. Source: Duff & Phelps. Justification:...

Terminal Value: Gordon Growth 4%. Capex = Depreciation in terminal year + 28.2% higher in explicit period per Tax Court precedent.

Do you want me to generate this as a formal 15-page Word / PDF document with Cover Page, Index, Detailed Sections, Case Law Annexure, and Editable Assumption Log Table for your company/project?