Actually the name of the 4th gen section should probably be re titled to 2009-2019. The 2019 classic is definitely a 4th gen in every way, if I posted a picture of a 2017 and a 2019 classic, you wouldn't be able to tell me which one was which (outside of the "classic" badge). Post that same 2017 picture with a 2019 or 2020 non classic, and it's completely different and obvious they are different generations. They kept making the 4th gen and labeled it "classic" to run concurrently with the release of the new body style 5th gen.
Even for ordering parts, you'll be a lot easier off just buying parts for a 2018 rather than potentially getting the wrong parts. Unless I'm missing something here, but you did say you had the classic, right?