Q. on supplemental deed of mortgage

Mr. A executed a supplemental deed of mortgage on 1/8/2011 in favour of a PSU bank for securing a term loan of Rs. 10 crore advanced by the bank to him. The requisite stamp duty was paid in toto by Mr. A. However the Supplemental mortgage deed was not registered. By "supplemental" it is meant that the said mortgage deed creates a mortgage kn those properties which have already been provided for as collateral security in respect of other loans advanced by the same PSU bank to Mr. A on earlier occassions. The question before Mr. A is :
Q1 can the said supplemental deed of mortgage be registered now?
Q2 if yes, what are the additional requirements to be followed by law?
Q3 is the document admissible as evidence in a court of law without being registered?
Q4 will registration if done now render the document valid and enforceable?