It can be. You will only be able to obtain a Medallion Signature Guarantee from us if you have proof of the holding. Furthermore, if you are not sure of the number of shares held and draft the necessary papers in accordance with what you believe the holding to be, you run the risk of not dealing with the whole shareholding during the transaction.
If further shares are later confirmed, you will usually have to go through the whole procedure again to deal with the additional shares. Our International Private Client team can, in most instances, arrange for confirmation of the shares with the North American transfer agent.