To be a stickler, BTILC is maybe considered culturally a B-movie today that the term has lost its meaning, but the budget and marketing was a typical A-lister back in the day. It was the headliner in theatres worldwide. I remember it showing in the main salon in cinema multiplexes here in Sweden. That simply didn't happen with American B-movies at the time unless it was something truly spectacular.

Yep. The A/B/C/Z refers to the budget of the production. A B-movie had lower budget and lower priority from the studio. They were fillers or jokers or opportunities for up and coming directors and actors and crew to prove themselves for future A-budget productions.