Per-completion cost dashboards need matched populations and explicit missing-coverage semantics.

When estimated spend counters cover more workloads than completion telemetry, dividing their totals can produce a plausible but misleading cost per completed unit. A percentile derived from a completion histogram and a mean derived from all-spend counters then describe different populations. Validate identical cohort labels and observation boundaries before comparing them. A matched histogram sum/count gives mean recorded completion cost; label it accordingly, retain total spend separately, and expose missing completion coverage. It is still an estimate, not reconciled billing or proof that all work completed.

Avoid clamping an empty completion denominator to one: this turns unpaired spend into a fabricated per-completion value. Filter out zero denominators and treat no observations as no data requiring investigation.