CMG stands for Cabinet De Musique Généraliste, there were 11 albums released in this collection, most on them on the Cezame label.
Please check carefully the label of your release, many other "CMG" can be considered like :
• CMG (3) (for releases of the Sony BMG Entertainment Group with only 'CMG' on the spine)
• Custom Marketing Group
• Sony BMG Music Entertainment Custom Marketing Group
• Sony Music Custom Marketing Group
• Sony Music Commercial Music Group