# Relationship history for MSHA mine 1900505

Current hierarchy: **Ian S Norrie → Plympton Sand & Gravel Corp → Plympton Sand & Gravel Corporation**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-18T09:31:49.615908+00:00

## Valid-time edges

- **operator_operates_mine:** Plympton Sand & Gravel Corp → Plympton Sand & Gravel Corporation; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** John W Norrie → Plympton Sand & Gravel Corporation; 1950-01-01 to 2026-07-13; source msha-controller-operator-history
- **controller_controls_operator:** John W Norrie → Plympton Sand & Gravel Corp; 1950-01-01 to 2026-07-13; source msha-controller-operator-history
- **controller_controls_mine:** Ian S Norrie → Plympton Sand & Gravel Corporation; 2026-07-14 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Ian S Norrie → Plympton Sand & Gravel Corp; 2026-07-14 to current/open; source msha-controller-operator-history