Boy did i learn a lot in a year LOL.
I started a new world in 1.14 an learned that weird stuff does indeed happen with even the slightest of chages to using the seed to make another world.
1 - if you use the seed you have to also keep all the settings exactly the same including the world name otherwise it will generate differently. you can change the name and other things after the initial save.
2 - if you update the version to a much higher version, like from 1.14 to 1.16, things will change even in the chunks that are already loaded. a villager was talking to a nitwit before the update and after it was relaoded the nitwit was gone but the villager was still in place as if still talking for a second or 2 before walking away, among other things.
3 - as always you have to make the copy world in the same version as the original was made. You cant use the seed that was made in 1.14 and make it in 1.15 or 1.16 the world will generate differently.
does anyone know of any program that can compare two worlds to see the differences of the same seed used in two different versions. im curious about things like that. i know of programs that can compare the code but what fun is that LOL