Sometimes a transfer agent may require information in a slightly different format than included on a subscription agreement. For example ""John Smith as trustee for the Smith Family Trust"" versus the subscriber signed as ""The Smith Family Trust"".
It is the issuers choice whether they need to have a subscription agreement signed. Most issuers and their counsel take the position that, so long as the information is materially correct and the subscriber is identifiable, the subscription agreement is a duly formed contract, and the additional information can be collected outside of the subscription agreement. You may wish to consult with legal counsel as to what is best in your particular circumstance.