The ChangeStream::CURSOR_NOT_FOUND constant was introduced in d1cd6ef for PHPLIB-276 but it was only used for internal logic to determine whether an error was resumable.

2a288a0 for PHPLIB-351 later deprecated the constant, and then 35c1ac2 for PHPLIB-566 later introduced a private static property for the constant.

PHPLIB-1152 migrated private static to private const but was unable to do so for CURSOR_NOT_FOUND due to BC reasons. Therefore, this ticket will serve as a reminder to make it private in the next major version.