Live sizing on Westin: stair lifts ~254 customers / porch-VPL ~30 / lift chairs ~41, but lift serial coverage ~0 (12/416 stairlift lines). The serial-as-unit-key approach (valid for ADP wheelchairs) fails for lifts. Backfill now splits into two regimes: serial dedup for wheelchairs; partner+base-product+sale-line dedup for lifts with accessory-line exclusion via the per-product maintainable flag.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>