It was explained to me the difference of channeling and taking full trance. Channeling usually involves a semi-conscious state of mind. In the tradition of the Tibetan oracles, channeling of a higher being and this happens when the Tantric retreats are not complete or the oracle has been 'polluted'.
Therefore, the oracle may sometimes be conscious of what transpired during the channeling session and could sometimes be accused of misconstruing the line of communication of the higher being. The pollution here refers to engaging in activities or foods that blocks or interrupts the psychic channels. Therefore, channeling as such is not as encouraged especially with the State oracle, which have to deal with State secrets.
On the other hand, a full trance of a higher being would be effected when the oracle is totally unconscious. That would mean that his Tantric retreats and training has been completed and he has remained spiritually clean. Therefore, an oracle have to maintain a strict diet and also strict observance of various ritual restrictions. I don't fully know what the observances are but I do know it includes a clean Samaya with one's Guru and also the observance of the daily Tantric meditations, which is usually Yamantaka.
However, I know that the translations from Tibetan could be loose with both words and also not all writers know of the differences between them. Therefore, both words could be used interchangeably in some books and articles.