The visa, when living outside Schengen, was not per se a crew visa. It was meant to allow entry for company related training, ie a multiple entry visa. However it was a multiple entry visa valid again for one year. On every flight that overnighted in Schengen area her passport was stamped and checked on entry and exit.
For work in Europe, the country of our residence issued my wife a D-visa valid for one year at the time. That D-visa allowed her to spend 3 months in other Schengen countries no other visa needed.
I'll have to check what the visa letter code is when I get back home as I cannot remember anymore.