# Relationship history for MSHA mine 3304775

Current hierarchy: **National Lime & Stone Co. → NLS Asphalt, Inc. → Keestrack Frontier Screen**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-13T11:19:05.459773+00:00

## Valid-time edges

- **controller_controls_mine:** National Lime & Stone Co. → Keestrack Frontier Screen; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** National Lime & Stone Co. → Keestrack Frontier Screen; 2022-04-28 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** The National Lime and Stone Company → Keestrack Frontier Screen; 2022-05-03 to 2025-12-08; source msha-controller-operator-history
- **controller_controls_operator:** National Lime & Stone Co. → The National Lime and Stone Company; 2022-05-03 to 2025-12-08; source msha-controller-operator-history
- **operator_operates_mine:** NLS Asphalt, Inc. → Keestrack Frontier Screen; 2025-12-09 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** National Lime & Stone Co. → NLS Asphalt, Inc.; 2025-12-09 to current/open; source msha-controller-operator-history