Incorporating changes into bolt 11, rather than creating a completely new invoice format, ensures backward compatibility to some extent. Users encountering invoices with unfamiliar features will receive an error message indicating that the invoice uses an unknown required feature bit. This approach not only informs users about the nature of the error but also hints at the necessity for an update or adjustment in their current system to accommodate the new features. Such a method contrasts sharply with the introduction of a brand-new format, which could result in unparseable invoices and potentially greater confusion among users who are unaware of the change. The decision to build upon bolt 11 effectively leverages its existing infrastructure to facilitate a smoother transition to enhanced functionality, emphasizing the importance of user experience in the evolution of payment protocols.