5. The relief provided for in subdivision two of this section shall not be granted unless
a. the mortgage was executed after September 1, 1951, or
b.the defendant whose right title or interest will be extinguished by failure to redeem the property within the time fixed by the judgment held such right to redeem only by virtue of a subordinate mortgage or other lien, and an action to foreclose such right of redemption would not be barred at the time this act shall take effect.
The relief provided for in subdivision four of this section shall not be granted unless the improvements were made after September 1, 1951, except to the extent that a recovery, allowance or credit for or on account of the value of any improvements, including improvements made prior to the effective date of this act, might be granted, in any other action or proceeding, to the person maintaining the action provided for in section 1503.