You're not missing anything. The key is this sentence "If the product you sold turns out to be faulty — or doesn't look or work as advertised — within the timeframe of the legal guarantee" - it's only when the product "turns out to be faulty" meaning - it has a manufacturing defect. It's defined exactly in the text of the legislation, would need to dig it out. If the product doesn't have a manufacturing defect, it "just" stops working at 23 months mark, the seller isn't legally required to fix it, unless you can prove that it's due to a manufacturing defect.

>> I've seen in the past regional sellers that claimed that their provide a shorter guarantee.

The sellers have to provide that guarantee against manufacturing defects for a minimum of 2 years, correct. Manufacturers can provide any length they like as they aren't the seller(in some cases and with some products they are legally bound as well, but it's not for everything - cars for instance have their own set of rules which bind the manufacturer not just the seller).