Update sim-swap.yaml

Improve documentation following @gregory1g suggestion.

code/API_definitions/sim-swap.yaml

@@ -30,9 +30,9 @@ info:
 
     - POST retrieve-date : Provides timestamp of latest SIM swap, if any, for a given phone number.
 
-      - If no swap has been performed, the API will return the SIM activation date (the timestamp of the first time that the SIM connected to the network).
+      - If no swap has been performed and the MNO supports unlimited SimSwap monitoring timeframe, the API will return the SIM activation date (the timestamp of the first time that the SIM connected to the network).
 
-      - If the latest SIM swap date (or the activation date if no SIM swap) cannot be communicated due to local regulations preventing the safekeeping of the information for longer than the stated period, a `null` value will be returned. Optionally, a `monitoredPeriod` could be provided to indicate that no SIM swap has occurred during this timeframe (in days).
+      - If the latest SIM swap date (or the activation date if no SIM swap) cannot be communicated due to local regulations (or MNO internal privacy policies) preventing the safekeeping of the information for longer than the stated period, a `null` value will be returned. Optionally, a `monitoredPeriod` could be provided to indicate monitored time frame (in days) supported by the MNO. In this case the response must be treated as "there was no sim swap events during 'monitoredPeriod'. Either the parameter is optional, it is recommended to support it in SimSwap implementations.
 
     - POST check: Checks if SIM swap has been performed during a past period (defined in the request with 'maxAge' attribute) for a given phone number.