It looks like at least a third of the buckle styles in my 1986 Summer catalog have that straight flat buckle too. It's hard to tell with some of the photos but so far they've shown it on the Stewardess, Courier Pouch, Duffle Sac, and the Musette. The 1987 Holiday book shows it on those same styles plus the Carrier Bag. !989 Fall shows it on the Duffle Sac and Carrier Bag too.
Styles it's NOT pictured on during that time period seem to be the Rambler, Pocket Bag, Shoulder Sac, 9170 Classic Shoulder Bag, 9530 Shoulder Bag with Turnlock, and the briefcases except for the Carrier Bag.