Usage summaries should group records using a clearly defined local date range and keep currencies separate. Counts, units and monetary values describe different facts.
Exact accumulation should precede invoice rounding. Display formatting must not rewrite stored amounts, and an acknowledgement must identify the complete transferred set.
A whole-period billed indicator should derive from durable success evidence rather than a manually editable flag. A submission without confirmed success must not imply completion. Retries should reuse the same intent and detect conflicting evidence.