Please check!

Hello

At the time of admission, the counsellors will verify the original mark sheet. However, in case the mark sheet has not been/ is not issued by the date of admission by the concerned examining body, Candidates will have to/ have to submit an undertaking to this effect.

Could you please check if the text is ok? Also, I'd be grateful if you help me with the correct tense choice in the two pairs- 1)has not been/ is not; 2)Will have to/ have to.

Please help!