I loaded several new worlds on a fresh Minecraft - i.e., I had all new data.
I started up one of these worlds, and I was greeted with one good chunk, and every other chunk visible was rendering repeated parts of chunks, cycling between cave systems, bedrock, and ground level, but the hitboxes suited it being part of the regular landscape. Also, entities were effected - I saw a mob that had the raw / base texture for a cave, with the actual textures not loaded, but just the base grey.