# C809 — Resolve the NT head-role dependence

## Question

Would the birth-hinge head produce the same BJ duration?

## Inputs

```json
{}
```

## Sources

```json
[
  "File43 Matthew birth-hinge2806 versus envelope2876"
]
```

## Opened utc

2026-09-28T02:09:09.616674+00:00

## Results

```json
{
  "birth_head": 2806,
  "envelope_head": 2876,
  "Luke_minus_birth": 2520,
  "Luke_minus_envelope": 2450,
  "role_effect": 70
}
```

## Finding

Using Matthew’s birth head gives2520; its head envelope gives2450. The interface therefore depends on an explicit source role, just as the BJ2450/2400 comparison depends on Creation/Fall roles.

## Reassessment

Specify which operations explain the BJ families and which source choices remain inputs.

## Checks

```json
{
  "birth2520": true,
  "envelope2450": true
}
```

## Closed utc

2026-09-28T02:09:09.617506+00:00

## Record provenance

Exact record hash: `3024e1b427420076a981e30a58b2c49a169b1500efe3af2116d9a23af259804b`

Source journal: `Research_Cycles/C0732_C0831/journal.json`