I have four generations of ortliebs:
- bungee elastic band and hook type from early 90s,
- maybe early 2000s maybe with tab but limited movement and straight shape single slot for it to slide in (not curved) bought em used so not sure of age
- single slot for tab but curved
- double curved slots, aka football ones
the second one, with straight shaped slot for tab to move in is the most restricted, i see why they improved it to curve and double curve football ones