Fix history wording

Author: LTA-Thinking

articles/healthcare-apis/fhir/export-data.md

@@ -65,7 +65,7 @@ The FHIR service supports the following query parameters for filtering exported
 | `_type` | Yes | Allows you to specify which types of resources will be included. For example, `_type=Patient` would return only patient resources.|
 | `_typeFilter` | Yes | To request finer-grained filtering, you can use `_typeFilter` along with the `_type` parameter. The value of the `_typeFilter` parameter is a comma-separated list of FHIR queries that further limit the results. |
 | `_container` | No |  Specifies the name of the container in the configured storage account where the data should be exported. If a container is specified, the data will be exported into a folder in that container. If the container isn't specified, the data will be exported to a new container with an autogenerated name. |
-| `_till` | No |  Allows you to export resources that have been modified till the specified time. This parameter is applicable only with System-Level export. In this case, if historical versions exist, export guarantees true snapshot view, or, in other words, enables time travel. |
+| `_till` | No |  Allows you to export resources that have been modified till the specified time. This parameter is applicable only with System-Level export. In this case, if historical versions have not been disabled or purged, export guarantees true snapshot view, or, in other words, enables time travel. |
 
 > [!Note]
 > Only storage accounts in the same subscription as the FHIR service are allowed to be registered as the destination for `$export` operations.