fix(historian): #681 re-review — OpcQuality low-byte comparison, no-data boundary quality is 1

docs/Historian.md

@@ -787,7 +787,7 @@ and evicts its shared historian session (see the HistorianGateway issue text in
   (histsdk evidence: `Quality = 133`, `OpcQuality = 192`) — the value in effect there, not a stored sample. Starting 1 ms early puts
   that row outside every bucket. A pre-window row only proves "the tag has earlier data" (start-of-data Partial, Count's in-range
   zero), and only when its **OPC quality is not Bad** — a "no earlier data" NULL row still carries a value on the wire (histsdk sets
-  `NumericValue = 0` on every numeric row and `StringValue = ""` on a string one) but with OPC quality 0.
+  `NumericValue = 0` on every numeric row and `StringValue = ""` on a string one) but with a Bad OPC quality (captured as 1, no-data; histsdk string-read-layout.md).
 - **Earlier-data probe.** When the data range matters (every per-sample aggregate but `Average`) and no non-Bad pre-window row
   arrived, a 2-row read `[1970-01-01, start)` asks whether the tag has data before the window. Normally this fires only for a tag
   whose history really begins inside the window.