Which of the following can lead to a later buyer obtaining good title to a patent?

The reason option C is correct is that a later buyer who was unaware of a prior sale and compensated for the patent may be able to obtain good title based on the principle of good faith purchasers. In patent law, a buyer who acquires a patent without knowledge of a prior conflicting interest and who pays value for the patent typically is protected, provided that the previous owner did not record the assignment in a timely manner. This principle recognizes the interests of buyers who, acting in good faith and without knowledge of prior claims, secure a transfer that is valid in the eyes of the law.

In contrast, the other choices do not support a later buyer obtaining good title. For example, if the later buyer pays nothing, they have not provided any consideration that generally is necessary for a valid transfer. If the first buyer records the assignment after 3 months, this could imply that the later buyer does not have a strong claim, depending on the jurisdictional rules governing recording notices. Finally, needing special permission to buy the patent usually indicates potential legal complications that could affect the validity of the sale, rather than establishing a straightforward transfer of title.