Yaarel
🇮🇱He-Mage
Old school often used the 1e core with 2e supplements.They have a different design philosophy, and are labeled as separate editions, so they are separate. I mostly used the core rules for 1e and the supplements for 2e when we played. We did that from '88 to '14, with a brief hiatus in '01 for 3e, and in '10 for 4e.
Now might be the other way around.
Players use the 2024 core with 2014 supplements.
Because the schedule for new D&D books will probably continue to be slow, players will continue to rely on 2014 content for years.
I am sorry for your loss of your friend.Then we switched to 5e until '18 when my friend passed away and the group broke up. I've been flailing ever since.