"those are small details, the core of our beliefs hasn't changed."
Uhm...
In the beginning Charles Russell was the faithful slave.
Now he's not!
In the beginning Armageddon would be here by 1914.
Now it won't
In the beginning we prayed to and worshipped Jesus.
Now we don't
These and many other core teachings have been gutted from Watchtower's foundational teachings. I guess they have it in their minds that whatever teachings were lucky enough not to get the axe over the last 130 years constitute core teachings.