The medium/large size (the classic size) always did have the double flap only, unless it was a rare or special model of the flap bag. I believe up until 2010, the jumbos and maxis only came in single flaps, and from 2010 and afterwards, the jumbos and maxis started coming out in double flaps only. I didn't start buying Chanel until this year (though I would have if I could have years and years ago), but from what I have read on here, it seems that the quality started going down around the same time they stopped making bags with gold-plated hardware and single flaps.
I much prefer the double flap as well. It is the way Coco Chanel originally designed it, and I love the compartmentalizations of the bag with the double flap, rather than the simple bucket-like interiors of the single flaps (though they are still beautiful). The double flap also holds the structure of the bag better.
Either way, I'm sure you will be happy with the bag
