First example: Yes. If you make a NEW theme (that is copy a theme to a new folder and change that, OR via child theming), then YOUR theme will NEVER be overwritten.
Second example: Again, yes.
Seriously, I don't know what other way to tell you this, and two (three!) of us have told you. YOUR themes, in their OWN folder, be they a total copy of the parent theme OR a child theme of the parent, will NEVER EVER be overwritten by either the WP upgrade OR the parent theme upgrade.
By 'core' what we meant was 'The core CODE that makes up WP.' Not the themes.
Core = code, and can be overwritten by plugins and functions you put in your theme.
Themes = look/feel of your site, and can be customized and never overwritten, by child themes or theme copying.