Why does the list of Outline Numbering options (in the Outline Numbering
Gallery) change depending on which 'Style' of text I'm looking at?

For example, I want to apply the same Outline Numbering to Heading 1 as to
Heading 2. So I set up the Outline Numbering for the Heading 1 style
(including that level 1 is attached to Heading 1 and level 2 is attached to
Heading 2). I've also set up the tabs and indents the way that I want them.

Now, when I modify the Heading 2 style, I cannot select the same outline
numbering configuration that I've already created. I have to recreat it for
each Heading style (I've got up to 4).

Just a note, that these are custom heading styles that I'm creating because
they are in my Appendix, so I don't want them included in the Table of
Contents. I've been calling them 'Heading 1 Appendix' etc.

As a general comment, I've always found the customization of outline
numbering to be overly difficult, and that Word will often 'fight back' and
change things after I've already created them.

Thanks for your help,
KB