This is primarily due to timing differences. Mortgage providers may not pass the revenue stream received from customers to holders of mortgage pass-through securities immediately after receipt. This delay can cause a discrepancy between the cash flows generated by the underlying pool of mortgages and the cash flows forwarded to the investors of the pass-through security. Therefore, it is not accurate to say that these cash flows 'exactly match'.

Choice A is incorrect. Mortgage pass-through securities indeed represent investors' claim against a pool of mortgages. This means that the investors have a right to receive payments from the pool of mortgages that back the security.

Choice B is incorrect. It's true that all investors in one pool receive the same return. The rate of return on mortgage pass-through securities is typically equal for all investors as they all share in the interest and principal payments from the underlying mortgage pool.

Choice D is incorrect. Pass-through securities do have prepayment risk, which refers to the risk that borrowers may pay off their mortgages earlier than expected, usually when interest rates fall. This can reduce future cash flows for investors as they will not receive as much interest income over time.