What information should I put for the Country/Territory boarded, flight number, and visa number in the TDAC form when coming to Thailand?

This post addresses questions regarding how to fill out the TDAC (Thailand Declaration Arrival Card) form when entering Thailand, particularly about listing the country of boarding, the flight number, and the visa number. Multiple comments suggest that when filling out the form, travelers can use the departure country of their last flight or the last country they were in before arriving in Thailand, as it is not strictly enforced. Furthermore, the flight number can correspond to either the departing flight or the last flight taken to Thailand, and the visa number field is not mandatory and can often be left blank.