Only source from Chiang Mai to Bangkok "means that this particular cycle is the only source of Chiang Mai if you do not have a note indicating that the session is both depart from Bangkok and depart from Chiang Mai.
A source from Chiang Mai to Bangkok, "this means that the only available source of Chiang Mai only if no note. Show that around the time that is available for both arrivals and departures from Chiang Mai to Bangkok.
The origin of Chiang Mai.) "means that this round only offer the origin of Chiang Mai only if no note. Show around the time of the departure from Bangkok and departing from Chiang Mai.