Abandonment Rio Grande San Juan Alamosa Durango

I am curious that when I search the forum on the word "abandonment", I do not actually find many results, and the results I do find are actually just in the last few months. Does anyone know more about the regulatory and legal issues in the abandonment of the San Juan Extension? For example, what rules guided when the Rio Grande was required to offer service? I read that service was essentially twice monthly in 1968. How was that determined? Was there an agreement with the ICC? And then, the last service was in August 1968 as stated, but abandonment was not final until December of the following year. So why was there no service in 1969? What is the difference between refusing service and abandonment?