In computing loan insurance benefits, the date of default shall be considered as:

(a) The date of the lender's acceleration of the debt because of the borrower's uncorrected failure to perform a covenant or obligation under the note or security instrument; or

(b) The date of the first failure to make a monthly payment which subsequent payments by the borrower are insufficient to cover when applied to the overdue monthly payments in the order in which they become due.

(c) The date of the lender's acceleration of the debt because of the borrower's default under the first conventional note and mortgage.