It sounds like the existence of an evidence submission itself, let alone the documents therein, could be kept confidential until NICE guidance (and/or NICE draft guidance)?
No chance. NICE is extremely diligent in updating public records of where they are at in the appraisal process. We would see updates to their 'in development projects database' well before they issue guidance. This link: DCVax-L for treating glioblastoma [ID836]