Extension Number missing from APi calls

var ExtParameters = new ListExtensionsParameters();

ExtParameters.perPage = 1000;

var extensionList = await rc.Restapi().Account().Extension().List(ExtParameters);

We used above API call to get all extensions company wide. But we are missing one extension even if that extension is in the call log(whole company wide) data through API. Is there any conditions for which an extension will not be fetched by the API?