diff --git a/skills/last9-cloudwatch/SKILL.md b/skills/last9-cloudwatch/SKILL.md
index f34a6c4..8a8933a 100644
--- a/skills/last9-cloudwatch/SKILL.md
+++ b/skills/last9-cloudwatch/SKILL.md
@@ -47,7 +47,7 @@ Installed schemas take precedence over this reference:
 | `prometheus_instant_query` | `query`, `datasource`, `time_iso` |
 | `prometheus_range_query` | `query`, `datasource`, `start_time_iso`, `end_time_iso` |
 
-Discover names with `label: "__name__"`. Do not invent a `step` parameter. Distinguish raw range selectors evaluated once from repeatedly evaluated charts.
+Discover names with `label: "__name__"`. Do not invent a `step` parameter. Distinguish raw range selectors evaluated once from repeatedly evaluated charts. A selector carrying no range returns only the latest period, so any total, average, or coverage claim about a whole interval needs a range selector spanning that interval; before claiming one, check that the returned sample count matches the periods the interval should contain.
 
 ## Discover and execute efficiently
 
diff --git a/skills/last9-cloudwatch/references/msk.md b/skills/last9-cloudwatch/references/msk.md
index 8f25e37..15d068c 100644
--- a/skills/last9-cloudwatch/references/msk.md
+++ b/skills/last9-cloudwatch/references/msk.md
@@ -10,7 +10,7 @@ Broker metrics, cluster aggregates, and topic breakdowns are not interchangeable
 
 ## Throughput and lag
 
-- `BytesInPerSec`, `BytesOutPerSec`, and `MessagesInPerSec` already describe rates. Use the requested level or average; applying `rate()` again changes the quantity. Combining broker/topic rows needs a verified non-overlapping population.
+- `BytesInPerSec`, `BytesOutPerSec`, and `MessagesInPerSec` already describe rates, so applying `rate()` again changes the quantity. Match the average to the requested window: for the latest period use that matched Sum/SampleCount pair; for a mean over the requested interval use total Sum / total SampleCount across the disjoint periods, read from the raw companion series over that window rather than a single instant query returning only the last period. Combining broker/topic rows needs a verified non-overlapping population.
 - `MaxOffsetLag` is the maximum offset lag across the applicable partitions; `SumOffsetLag` is a different aggregate. Neither is a count of unique messages processed during the observation window.
 - `EstimatedMaxTimeLag` is in seconds. An offset count cannot be converted to time without additional evidence.