Why Hindsight Cannot Cure Planning Decision Failures

When a planning decision is challenged, it is common for authorities to rely on material produced after the decision in order to defend what was done earlier. This reliance is often framed as clarification, confirmation, or completion of work that was “already understood”.

This page explains why such post-decision material cannot retrospectively cure evidential absence at the time a planning decision was taken.

It does not assess planning merits or outcomes.
It does not determine whether a decision was lawful or unlawful.
It explains why hindsight cannot be substituted for decision-stage evidence.

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The problem hindsight creates

Once a decision has been questioned — whether through complaint, appeal, or judicial review — there is a strong institutional incentive to reconstruct the decision as reasonable, informed, and complete.

This reconstruction typically relies on material that:

• was produced after the decision was taken;
• was not before the decision-maker at the time; or
• resolves matters that were previously deferred or unassessed.

When this material is treated as if it had existed earlier, the distinction between decision-stage evidence and later justification collapses.

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Decision-stage evidence and post-decision material

A planning decision must be assessed by reference to the information available at the moment the decision was taken.

Material produced after that point may be:

• technically sound;
• professionally competent;
• relevant to future stages; or
• useful for other regulatory purposes.

However, none of these qualities convert post-decision material into decision-stage evidence.

If evidence did not exist at the time of decision, its later production does not alter that fact.

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Why later evidence cannot “confirm” earlier sufficiency

Authorities sometimes argue that later evidence merely confirms conclusions that were already implicit or understood at the time of decision.

This argument fails because confirmation presupposes the prior existence of assessed conclusions. Where no completed assessment existed, there was nothing capable of being confirmed.

Later evidence does not demonstrate that the decision-maker had sufficient information earlier. It demonstrates that the information was obtained after the decision was taken.

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Hindsight and deferred assessment

Reliance on hindsight most commonly arises where assessment was deferred, whether explicitly or implicitly.

Indicators of deferral include:

• statements that issues will be addressed by condition;
• references to future reserved matters;
• acceptance of outline proposals without resolved impacts;
• absence of completed technical conclusions at determination.

Where assessment is deferred, later evidence does not cure the deferral. It confirms that the decision was taken without the evidence in question.

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Why hindsight is incompatible with accountability

Allowing later material to be treated as if it had existed earlier undermines the principle that decisions must be justified by reference to what was known at the time they were made.

If hindsight were permitted to cure evidential absence:

• any decision could be defended after the event;
• decision-stage scrutiny would become meaningless;
• the evidential record would no longer be fixed in time.

Accountability depends on a stable evidential boundary. Hindsight dissolves that boundary.

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Appeals, judicial review, and hindsight

In appeal and judicial review contexts, the question is not whether later evidence supports the outcome that was reached.

The question is whether the decision-maker had sufficient evidence at the time to lawfully reach that outcome.

Post-decision material may explain how a proposal could be made acceptable. It cannot explain how the decision was lawfully taken without that evidence.

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Fixing the boundary

This page does not argue that later evidence is irrelevant in all contexts.

Its purpose is narrower: to fix the boundary between decision-stage evidence and later narrative, and to explain why that boundary cannot be crossed.

Once a decision has been taken, the evidential record is closed. What follows may inform future action, but it cannot rewrite the past.

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Summary

Evidence produced after a planning decision does not become decision-stage evidence.

Later material cannot confirm, complete, or cure evidential absence at the time of decision.

Hindsight explains outcomes; it does not justify decisions.

Planning accountability depends on what was known when the decision was made — not what was discovered afterwards.

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This page has been accessed 5 times. | Last edited 19 January 2026

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