아래와 다른 질문입니다.

토마토 실전 RC 100제 17쪽 151번에 관한 질문입니다.

Making a Difference Together

This weekend, the Halloway Helping Hands, more commonly known as Triple-H, is sponsoring its
annual cleanup project. This year, the group plans to focus on (restoring) Clearview Park, which has suffered
from underfunding and neglect over the past few years. Volunteers will clean up trash, repair broken equipment,
remove graffiti, and plant flowers. The event will begin at 10 A.M. on Saturday and continue throught the weekend.

Triple-H, a non-profit organization aimed at improving the community, was started ten years ago by five schoolteachers. ( Since then / Until now ), its membership has grown to nearly 100 volunteers, and new members are always welcome.
Volunteers who are not formal members are also encouraged to participate in any projects the group sponsors.
If you would like to join the (initiative) to make Halloway a cleaner and more beautiful place to live, call the enrollment coordintor, Audrey Watts, at (605) 555-2840

강의에서 Since then 과 Until now 모두 정답이 될 수 있다고 하셨는데요,

Since then이 되는 이유는 설명을 해주셨는데, Until now도 될 수 있는 이유에 대해서 좀 더 부가적인 설명을 듣고 싶습니다.

또한 강의에서는 출판사에 전화를 해보신다고 하셨는데, 이에 대해서는 어떻게 답변을 들었는지도 궁금합니다.