When I look at the in app purchase prices on the App Store page, it tells me what they’re for? (1 month vs 1 year). You can usually assume that if you see a different price for the same name item, that it’s a sale price.
The premium yearly subscription has 3 price points shown (22.99, 34.99 and 44.99€) - I feel really bad for the developer as their customers are reminded that they have to pay more than others have paid before. I don't get why Apple is showing the old prices.