The one on the left with the fluted CS and hook was probably made in the early 90s during the transition years between the late 80s style of fluted CS and no hook and the 90s style of solid CS and hook. You see lots of interesting combos from this time as they introduced new parts while using up old inventory.
Yeah there are "official" dates when things were introduced, but tool changes like the solid CS (or the scissors rivet or the new metal file) are usually backwards compatible. Victorinox isn't like a car company that has to shut down, retool, and come back up producing a new model. For things like the solid CS, they make the decision to change design and one day the assemblers open boxes with the new tool and start using that. Find a box of old CS in the back? Maybe a few rogue CSs fell into another bin? Waste not want not - throw them on a knife an move on. They're not a mint concerned with everything being "proper for the year of production" - they're a high volume knife maker whose goal is to make as many knives for as little cost as possible. Not using an older CS that you found hidden in the bottom of a tub of caplifters would be wasteful so they just use it.
Since you don't show many pictures of the one on the right, I'm going to throw out a few guesses, in order of likelyhood:
1. It's a pre-1990 economy model Huntsman. Economy models never had fluted corkscrews, even back to their introduction in the 1970s.
2. It's a pre-1990 premium line "Victorinox" Huntsman model that should have had a fluted corkscrew, but the assembler used a economy line corkscrew by mistake and it slipped through QA. It happens.
3. It's a post 1992 repair of a pre-1990 knife. Since the smooth CS is backwards compatible, they just used that.