I recommend you the reading of the Programming without SDK Tutorial. You should find the answer you need in the Managing the HTTP responses section (it contains a link to the exhaustive list of codes). In a nutshell, 200 means the data extraction is complete, 202 means it is pending.
Please, read this great tutorial for more details. It is available in the DataScope Select - REST API page where you'll find tons of other excellent learning materials.
The codes can be found on page: https://hosted.datascopeapi.reuters.com/RestApi.Help/Home/Index, or to navigate to this page, by going through your DSS GUI: 'Help' > 'REST API Help' > 'SDK' > 'Status Codes' (DSS credentials required).
The REST API uses HTTP status codes consistent with the OData protocol specifications.The status codes are documented in the DSS server help pages. The ones you will most frequently encounter are 200, 202, 204 and 401.