# C1547 — Trace theMT/LXX prefix difference to Lamech

## Question

Which source lifespan causes the20-year prefix difference?

## Sources

```json
[
  "File18.md selected753 decision",
  "File51a.md roundingrule"
]
```

## Opened utc

2026-09-29T02:37:40.585065+00:00

## Results

```json
{
  "rounded_differences": [
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    -20
  ],
  "actual_Lamech": [
    777,
    753
  ],
  "rounded_Lamech": [
    775,
    755
  ],
  "prefixes": [
    7620,
    7600
  ]
}
```

## Finding

The first eight rounded preNoah lives agree; selected Lamech775 versus755 accounts for the entire−20 prefix difference.

## Reassessment

Inspect how that small difference changes the retained trailing-zero register.

## Checks

```json
{}
```

## Closed utc

2026-09-29T02:37:40.585339+00:00

## Record provenance

Exact record hash: `eb46cb62e228fef440399b09dad7a03500cf921a95c557f53f8ae01e37004eea`

Source journal: `Research_Cycles/C1483_C1582/c1483_c1582/journal.json`