Following up by conducting an interview with a Jamb Officer,

No result yet - means that the results have not been processed by Jamb for reasons best know by the body. The truth however about this case is that there is a very great chance of the result being released in the next 2 weeks.

Withheld for Further Screening - Means that there were reports submitted to Jamb that a center or candidate was involved in malpractice and so the body is investigating on the validity of the report. If the centre or candidate is found guilty, the result will be seized. However if the case is resolved and no issues were found, the result will be released. No definite time to check but usually 2 weeks too.

You CANNOT See Your Result because "You ..." - If you result falls in this category. That's it. Nothing for you. Think of writing the next Jamb.