Hello,
Dig you change your request at all when you got a different number of results? How did you look up the expected number of results? Are you sure you're only counting TextAds?
One thing that may prevent some ads from returning is if they're in the Shared Library. That is a web interface only feature that is not supported by the AdWords API, so anything that's in the Shared Library will not be returned or counted by the API.
If that isn't the cause, please include your SOAP request so that I can take a look at what might be going on. Make sure to remove any private information.
Regards,
Mike, AdWords API Team