Immature years do not get a free pass to chain ladder. They need an a priori that you can defend.

Twelve months of development is not a stability story. Cape Cod and Bornhuetter Ferguson pull the ultimate toward the a priori when the triangle is thin.

State the a priori loss ratio, the earned premium timing, and why Cape Cod moved relative to BF.

A practical weighting pattern

Mature years can lean on chain ladder. Mid years mix BF and Cape Cod. The newest year often sits on a priori until paid development arrives.

Frequency severity is a check, not a substitute when exposure is off level.

Record at minimum:

• A priori loss ratio and source
• Earned premium on level notes
• BF weight
• Cape Cod weight
• Competing ultimates shown side by side
• What would change the weights next quarter

When paid runs ahead of the five-year average, say so in the reason. Do not hide it in a chart title.

The signing actuary still chooses. The production system only makes the competing numbers hard to ignore.

Thin development is not uncertainty theater. It is a reason to weight the a priori, written down.

That is how immature years stop being a black box.

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