Your question is rather complex. If the policy was issued as an employee benefit, then it falls under a federal law known as ERISA - the Employee Retirement Income Security Act - and preempts state law. From your question, it sounds like the life insurance policy was issued as an employee benefit. Under ERISA, if misrepresentations were made to your mother that reasonably caused her to forego obtaining life insurance coverage, the measure of damages would be the difference between the price for coverage at the time of the misrepresentation and the current price for an identical life insurance policy, plus attorneys fees and costs.
In a litigation context, to confirm that the policy received is identical to the policy in force at the time, you would simply have the insurer or employer swear that it is. Outside of a litigation context, there is really nothing you can do to confirm that it is the same other than ask that the insurer represent that it is to you in writing. Another option might be to try to discover some old policies from that time period from other employees,