The 14-3-1966 (March 14, 1966) date is the date of approval of the Cyclomoteur 3800 motor type, not the date of manufacture. Production and sales of the S 3800 started two months later in May of 1966.
Attached is a photo of where to look for the motor number. When you find the number, let me know what it is and I will tell you what you have. Be aware that 99% of the charts online are for Solexes sold in France, not in America or elsewhere.