Well, that depends on how many fewer units and how much higher a price. If they convert 100,000 users to 2024 at $19.99 but they would have converted only 60,000 users at $29.99, they're better off at the lower price point. Whatever the price is will be determined by what existing users are willing to pay for the upgrade. With the physical books, it doesn't matter if you have 2014 or not, but with digital, the levers they have grow. And keep in mind that for the first few months of release, getting conversions may be worth more to them than a few extra $ in their pocket.
That said, the price points I suggested may be too low. Maybe $30, $25 and $20 would be more reasonable.